NASA

'Reference

Publication

1228

March 1990

. _-

Fastener Design Manual

Richard T. Barrett

. , :. ? .

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NASA

Reference

Publication

1228

1990

National Aeronautics and

Space Administration

Office of Management

Scientific and Technical

Information Division

Fastener Design Manual

Richard T. Barrett

Lewis Research Center

Cleveland, Ohio
ERRATA 

NASA Reference Publication 1228 

Fastener Design Manual 

Richard T. Barrett 

March 1990 

The manual describes various platings that may be used for corrosion control including cadmium 

and zinc plating. It does not mention outgassing problems caused by the relatively high vapor 

pressure of these metals. The fastener manual was intended primarily for aeronautical applications, where outgassing is typically not a concern. 

 Issued June 17, 2008 
Summary . . . .. . . . . .. .. . .. .. . . . .. . . . . .. .. . .. .. . .. .. . .. .. . .. . . . .. . . . .. . . .. . . . .. . . . . .. .. .. . .. .. .. . .. .. .. . .. .. . .. . . . .. . . .

Introduction . .. .. . . . .. . . . . .. . . . .. .. . . . .. . .. .. . .. .. . .. .. . .. .. . .. .. . .. .. . .. . . . .. .. . .. . . . .. .. .. . .. .. .. . .. .. . .. . . .. . . . .. .

General Design Information

Fastener Materials . . .. .. . . . .. . .. . .. .. . .. .. . .. .. . .. .. . .. . . .. . . . .. . . . .. . .. .. . . . .. . .. .. . .. . . .. . .. .. . .. . . .. . .. .. . .. ..

Platings and Coatings . .. .. . .. .. . .. .. . . . .. . .. .. . .. .. . .. .. . .. .. . .. .. . .. . . . .. . . .. . .. .. . .. .. . .. . . .. . .. .. . .. . . .. . . . ..

Thread Lubricants . .. .. . . . .. . . . . .. . . .. . . . . .. .. . .. . . .. . . . . .. . . .. . .. .. . . . .. . .. .. . .. . . . .. . . .. . .. .. .. . .. .. . .. .. . .. .. . .

Corrosion .. . . . . .. .. . .. .. . . . . .. . . . .. . . . .. .. . .. .. . .. .. . .. .. . .. .. . .. . . .. . .. . .. .. .. . .. .. . .. .. . .. . . .. . .. .. . .. . . . .. . . .. . .

Locking Methods . . . . . .. .. . . . .. . .. .. . . . .. . . . .. . .. .. . .. .. . . . .. . .. .. . .. .. . .. .. . .. .. . .. . . .. . .. .. . .. . . .. . .. .. . .. .. . .. .

Washers .. . . . . .. . . . .. .. . .. . .. . . . .. . . . .. . . . .. .. . .. .. . .. . . . .. .. . .. . . .. . .. . .. . . .. . .. .. . .. . . . .. . . .. . .. . . .. . . . .. . . . .. . .. .

Inserts .. . .. .. . . . . .. .. . .. .. . . . .. . . . . .. . . .. . . . . .. . . . .. . . . .. .. .. . . . .. . . . . .. .. .. . . . .. . .. .. . .. . . .. . .. .. . .. . . .. . .. .. . .. .. .

Threads . . . . . .. . . . . . . .. . . . .. .. . .. .. . .. .. . .. .. . .. .. . .. .. . .. .. . .. .. . .. . . . .. . . .. . . . . .. . . .. . .. .. . .. . . .. . .. . . . .. . . .. . .. .. .

Fatigue-Resistant Bolts . .. . .. . .. . . . .. . . . .. . . . .. . . . .. .. .. . .. .. . . . .. . .. .. . .. .. . .. . . . .. . . .. . .. .. . .. .. .. . .. . . . .. . . .. .

Fastener Torque . . .. .. . .. .. . . . . .. .. . .. . . . .. . . . .. . . . .. .. .. . . . . .. . . .. . . . .. . .. .. . . . .. . .. .. .. . . . .. . .. .. . .. .. .. . .. .. . ..

Design Criteria .. . . . . .. .. . .. .. . . . .. . .. .. . .. .. . . . .. . .. .. . .. .. . .. .. . .. . . . .. . . . .. . . .. . .. .. . .. . . .. . . . .. . .. .. .. . .. .. . ..

Rivets and Lockbolts

Rivets .. . .. .. . . . . .. . . . .. .. . . . . .. . . .. . . . .. . . . . .. . . .. . .. .. . . . .. . .. .. . .. .. . . . .. . .. . . . .. . . . .. . . .. . .. .. .. . . . .. . .. .. . .. . . . .

Lockbolts . .. . .. . . . . . .. . .. . . . .. . .. .. . . . .. . . . .. ... . . . .. .. . .. .. . . ... .. . . . . .. . . . .. . . .. . .. .. . .. .. . . .. . .. .. . .. .. . . . .. . . . .

General Guidelines for Selecting Rivets and Lockbolts . . . .. .. . .. . . .. . . . .. . .. .. . .. . . .. . .. .. . .. .. . .. . . .. . .

References .. .. . .. . .. .. . .. .. . . . .. . . . . .. . . . .. . . . .. . . . .. . . .. . . . .. . . . .. . .. .. . .. .. . . . .. . .. . . . .. . . .. . .. .. .. . .. .. . .. . . . .. . . .

.>

Appendixes

A—Bolthead Marking and Design Data . .. . . .. . . . .. . . . .. . .. .. . .. .. . .. .. . .. . . . .. . . .. . .. .. . .. .. .. . .. .. . .. . . .. .

B—Bolt Ultimate Shear and Tensile Strengths . . . .. . . . .. . . . .. .. .. . .. .. . .. .. . .. . . .. . . . .. . .. .. .. . .. .. . .. . . .. .

C—Blind Rivet Requirements . .. . . . .. . . . .. . .. .. . .. .. . .. .. . .. . . . .. . . . .. . . .. . .. .. . .. . . . .. . . .. . .. . . .. . . . .. . . . .. . ..

1

1

1

1

4

5

6

9

10

12

13

15

17

26

30

34

35

36

90

94

111
Summary

This manual was written for design engineers to enable them

to choose appropriate fasteners for their designs. Subject matter

includes fastener material selection, platings, lubricants,

corrosion, locking methods, washers, inserts, thread types and

classes, fatigue loading, and fastener torque. A section on

design criteria covers the derivation of torque formulas, loads

on a fastener group, combining simultaneous shear and tension

loads, pullout load for tapped holes, grip length, head styles,

and fastener strengths. The second half of this manual presents

general guidelines and selection criteria for rivets and

lockbolts .

Introduction

To the casual observer the selection of bolts, nuts, and rivets

for a design should be a simple task. In reality it is a difficult

task, requiring careful consideration of temperature, corrosion,

vibration, fatigue, initial preload, and many other factors.

The intent of this manual is to present enough data on bolt

and rivet materials, finishes, torques, and thread lubricants

to enable a designer to make a sensible selection for a particular

design. Locknuts, washers, locking methods, inserts, rivets,

and tapped holes are also covered.

General Design Information

Fastener Materials

Bolts can be made from many materials, but most bolts are

made of carbon steel, alloy steel, or stainless steel. Stainless

steels include both iron- and nickel-based chromium alloys.

Titanium and aluminum bolts have limited usage, primarily

in the aerospace industry.

Carbon steel is the cheapest and most common bolt material.

Most hardware stores sell carbon steel bolts, which are usually

zinc plated to resist corrosion. The typical ultimate strength

of this bolt material is 55 ksi.

An alloy steel is a high-strength carbon steel that can be heat

treated up to 300 ksi. However, it is not corrosion resistant

and must therefore have some type of coating to protect it from

corrosion. Aerospace alloy steel fasteners are usually cadmium

plated for corrosion protection.

Bolts of stainless steel (CRES)are available in a variety of

alloys with ultimate strengths from 70 to 220 ksi. The major

advantage of using CRES is that it normally requires no

protective coating and has a wider service temperature range

than plain carbon or alloy steels.

A partial listing of bolt materials is given in table I. The

following precautions are to be noted:

(1) The bolt plating material is usually the limiting factor

on maximum service temperature.

(2) Carbon steel and alloy steel are unsatisfactory (become

brittle) at temperatures below –65 “F.

(3) Hydrogen embrittlement is a problem with most

common methods of plating, unless special procedures are

used. (This subject is covered more fully in the corrosion

section.)

(4) Series 400 CREScontains only 12 percent chromium and

thus will corrode in some environments.

(5) The contact of dissimilar materials can create galvanic

corrosion, which can become a major problem. (Galvanic

corrosion is covered in a subsequent section of this manual. )

Platings and Coatings

Most plating processes are electrolytic and generate hydrogen. Thus, most plating processes require baking after plating

at a temperature well below the decomposition temperature

of the plating material to prevent hydrogen embrittlement.

However, heating the plating to its decomposition temperature

can generate free hydrogen again. Thus, exceeding the safe

operating temperature of the plating can cause premature

fastener failure due to hydrogen embrittlement as well as loss

of corrosion protection. (A summary of platings and coatings

is given in table II.)

Cadmium Plating

The most common aerospace fastener plating material is

cadmium. Plating is done by electrodeposition and is easy to

accomplish. However, cadmium-plated parts must be baked

at 375 “F for 23 hours, within 2 hours afier plating, to prevent

hydrogen embrittlement. Since cadmium melts at 600 ‘F, its

useful service temperature limit is 450 “F,
TABLE I.–SUMMARY OF FASTENER MATERIALS

Material

Carbon steel

Alloy steels

A-286 stainless

17-4PH

stainless

17-7PH

stainless

300 series

stainless

410, 416, and

430 stainless

U-2 12 stainless

Inconel 718

stainless

Inconel X-750

stainless

Waspalloy

stainless

Titanium

Zinc Plating

Surface

treatment

Zinc plate

Cadmium plate,

nickel plate,

zinc plate, or

chromium plate

Passivated per

MIL-S-5002

None

Passivated

Furnace oxidized

Passivated

Cleaned and

passivated per

MIL-S-5002

Passivated per

QQ-P-35 or

cadmium plated

None

None

None

Useful design

temperature

limit,

‘F

–65 to 250

–65 to

limiting

temperature

of plating

-423 to 1200

-300 to 600

-200 to 600

-423 to 800

-250 to 12W

1200

-423 to 900

or cadmium

plate limit

-320 to 1200

-423 to 1600

-350 to 500

Zinc is also a common type of plating. The hot-dip method

of zinc plating is known commercially as galvanizing. Zinc

can also be electrodeposited. Because zinc plating has a dull

finish, it is less pleasing in appearance than cadmium.

However, zinc is a sacrificial material. It will migrate to

uncoated areas that have had their plating scratched off, thus

continuing to provide corrosion resistance. Zinc may also be

applied cold as a zinc-rich paint. Zinc melts at 785 “F but has

a useful service temperature limit of 250 0F. (Its corrosioninhibiting qualities degrade above 140 “F. )

Phosphate Coatings

Steel or iron is phosphate coated by treating the material

surface with a diluted solution of phosphoric acid, usually by

submerging the part in a proprietary bath. The chemical

reaction forms a mildly protective layer of crystalline

phosphate. The three principal types of phosphate coatings are

2

Ultimate tensile

strength at room

temperature,

ksi

55 and up

up to 300

up to 220

up to 220

up to 220

70 to 140

Up to 180

185

up to 220

Up to 180

150

up to 160

Comments

Some can k

used at 900 “F

---------———————

Oxidation reduces

galling

47 ksi at 1200 “F;

will corrode

slightly

140 ksi at 1200 “F

136 ksi at 1200 “F

----- ——————-----

zinc, iron, and manganese. Phosphate-coated parts can be

readily painted, or they can be dipped in oil or wax to improve

their corrosion resistance, Fasteners are usually phosphate

with either zinc or manganese. Hydrogen embrittlement

seldom is present in phosphate parts. Phosphate coatings start

deteriorating at 225 “F (for heavy zinc) to 400 “F (for iron

phosphate).

Nickel Plating

Nickel plating, with or without a copper strike (thin plating),

is one of the oldest methods of preventing corrosion and

improving the appearance of steel and brass. Nickel plating

will tarnish unless it is followed by chromium plating. Nickel

plating is a more expensive process than cadmium or zinc

plating and also must be baked the same as cadmium after

plating to prevent hydrogen embrittlement. Nickel plating is

good to an operating temperature of 1100 “F, but is still not

frequently used for plating fasteners because of its cost.
TABLE11.–SUMMARYOF PLATINGSAND COATINGS

Type of coating

Cadmium

Zinc

Phosphates:

Manganese

Zinc

Iron

Chromium

Silver

Black oxide

(and oil)

Preoxidation

(CRES) fasteners

only

Nickel

SermaGard and

Sermatel W

Stalgard

Diffused nickelcadmium

Useful design

temperature limit,

“F

450

140 to 250

225

225 to 375

400

800 to 12W

1600

a300

1200

1100

450 to 1000

475

900

Remarks

Most common for aerospace

fasteners

Self-healing and cheaper

than cadmium

Mildly corrosion resistant

but main use is for surface

treatment prior to painting.

Another use is with oil or

wax for deterring corrosion,

Too expensive for most

applications other than

decorative

Most expensive coating

Ineffective in corrosion

prevention

Prevents freeze-up of cnEs

threads due to oxidation

after installation

More expensive than cadmium

or zinc

Dispersed aluminum particles

with chromates in a waterbased ceramic base coat

Proprietary organic and/or

organic-inorganic compund

used for corrosion resistance

and lubrication (in some cases)

Expensive and requires close

control to avoid hydrogen

damage

@il imillng point

Ion-Vapor-Deposited Aluminum Plating

Ion-vapor-deposited aluminum plating was developed by

McDonnell-Douglas for coating ~rcraft parts. It has some

advantages over cadmium plating:

(1) It creates no hydrogen embrittlement.

(2) It insulates against galvanic corrosion of dissimilar

materials.

(3) The coating is acceptable up to 925 “F.

(4) It can also be used for coating titanium and aluminums.

(5) No toxic byproducts are formed by the process.

It also has some disadvantages:

(1) Because the process must be done in a specially designed

vacuum chamber, it is quite expensive.

(2) Cadmium will outperform ion-vapor-deposited aluminum

in a salt-spray test.

Chromium Plating

Chromium plating is commonly used for automotive and

appliance decorative applications, but it is not common for

fasteners. Chromium-plated fasteners cost approximately as

much as stainless steel fasteners. Good chromium plating

requires both copper and nickel plating prior to chromium

plating. Chromium plating also has hydrogen embrittlement

problems. However, it is acceptable for maximum operating

temperatures of 800 to 1200 “F.

Sermatel W and SermaGard

Sermatel W and SermaGard are proprietary coatings 1

consisting of aluminum particles in an inorganic binder with

chromates added to inhibit corrosion. The coating material is

covered by AMS3 126A, and the procedure for applying it by

AMS2506. The coating is sprayed or dipped on the part and

cured at 650 “F. (SPSTechnologies has tested Sermatel Wcoated fasteners at 900 “F without degradation.) This coating

process prevents both hydrogen embrittlement and stress

corrosion, since the fastener is completely coated. Sermatel

is about as effective as cadmium plating in resisting corrosion

but costs about 15 percent more than cadmium. Fasteners are

not presently available “off the shelf” with Sermatel W or

SermaGard coating, but the company will do small orders for

fasteners or mechanical parts. These coatings will take up to

15 disassemblies in a threaded area without serious coating

degradation.

Stalgard

Stalgard is a proprietary coating3 process consisting of

organic coatings, inorganic-organic coatings, or both for

corrosion resistance. According to Stalgard test data their

coatings are superior to either cadmium or zinc plating in saltspray and weathering tests. Stalgard coatings also provide

galvanic corrosion protection. However, the maximum

operating temperature of these organic coatings is 475 0F.

Diffused Nickel-Cadmium Plating

This process was developed by the aerospace companies for

a higher temperature cadmium coating. A 0.0004 -in. -thick

nickel coating is plated on the substrate, followed by a

0.0002 -in. -thick. cadmium plate (per AMS2416). The part is

then baked for 1 hour at 645 “F. The resulting coating can

withstand 1000 “F. However, the nickel plate must completely

cover the part at all times to avoid cadmium damage to the

part. This process is expensive and requires close control.

1Sermatech International, Inc., Limerick, Pennsylvania.

ZJenkintown, Pennsylvania.

3EIc0 Industries, Rockford, Illinois.

3
Silver Plating TABLE 111.–SUMMARY OF THREAD LUBRICANTS

Silver plating is cost prohibitive for most fastener applications. The big exception is in the aerospace industry, where

silver-plated nuts are used on stairdess steel bolts. The silver

serves both as a corrosion deterrent and a dry lubricant. Silver

plating can be used to 1600 “F, and thus it is a good hightemperature lubricant. Since silver tarnishes from normal

atmospheric exposure, the silver-plated nuts are commonly

coated with clear wax to prevent tarnishing. Wax is a good

room-temperature lubricant. Therefore, the normal ‘‘dry

torque” values of the torque tables should be reduced by

50 percent to allow for this lubricant.

Passivation and Preoxidation

Stainless steel fasteners will create galvanic corrosion or

oxidation in a joint unless they are passivated or preoxidized

prior to assembly (ref. 1). Passivation is the formation of a

protective oxide coating on the steel by treating it briefly with

an acid. The oxide coating is almost inert. Preoxidization is

the formation of an oxide coating by exposing the fasteners

to approximately 13000 F temperature in an air furnace. The

surface formed is inert enough to prevent galling due to

galvanic corrosion.

Black Oxide Coating

Black oxide coating, combined with an oil film, does little

more than enhance the appearance of carbon steel fasteners.

The oil film is the only part of the coating that prevents

corrosion.

Thread Lubricants

Although there are many thread lubricants from which to

choose, only a few common ones are covered here. The most

common are oil, grease or wax, graphite, and molybdenum

disultide. There are also several proprietary lubricants such

as Never-Seez and Synergistic Coatings. Some thread-locking

compounds such as Loctite can also be used as lubricants for

a bolted assembly, particularly the compounds that allow the

bolts to be removed. A summary of thread lubricants is given

in table III.

Oil and Grease

Although oil and grease are the most common types of thread

lubricants, they are limited to an operating temperature not

much greater than 250 “F. (Above this temperature the oil

or grease will melt or boil off.) In addition, oil cannot be used

in a vacuum environment. However, oil and grease are good

for both lubrication and corrosion prevention as long as these

precautions are observed.

x

Type of lubricant Useful design

Oil or grease 250

Graphite

Molybdenum

disrdtide

Synergistic

Coatings

Neverseez

Silver Goop

a212to 250

750

500

2200

1500

&

Remarks

Most common; cannot be used in

vacuum

Cannot be used in vacuum

Can be used in vacuum

Can be used in vacuum

Because oil boils off, must be

applied after each hightemperature application

Do not use on aluminum or

magnesium parts; extremely

expensive

“Removable fastener” compounds

only

aCarrier bo,loff temperature,

Graphite

L‘Dry” graphite is really not dry. It is fine carbon powder

that needs moisture (usually oil or water) to become a

lubricant. Therefore, its maximum operating temperature is

limited to the boiling point of the oil or water. It also cannot

be used in a vacuum environment without losing its moisture.

Because dry graphite is an abrasive, its use is detrimental to

the bolted joint if the preceding limitations are exceeded.

Molybdenum Disulfide

Molybdenum disulfide is one of the most popular dry

lubricants. It can be used in a vacuum environment but

turns to molybdenum trisulfide at approximately 750 “F.

Molybdenum trisulfide is an abrasive rather than a lubricant.

Synergistic Coatings

These proprietary coatings4 are a type of fluorocarbon

injected and baked into a porous metal-matrix coating to give

both corrosion prevention and lubrication. However, the

maximum operating temperature given in their sales literature

is 500 “F. Synergistic Coatings will also operate in a vacuum

environment.

Neverseez

This proprietary compound5 is a petroleum-base lubricant

and anticorrodent that is satisfactory as a one-time lubricant

4General Magnaplate Corporation, Ventura, California.

sBo~ti~ Emhart, Broadview, Illinois.

4
up to 2200 “F, according to the manufacturer. The oil boils

off, but tie compound leaves nongalling oxides of nickel,

copper, and zinc between the threads. This allows the fastener

to be removed, but a new application is required each time

the fastener is installed. NASALewis personnel tested this

compound and found it to be satisfactory.

Silver Goop

Silver Goop is a proprietary compoundb containing 20 to

30 percent silver. Silver Goop can be used to 1500 “F, but

it is not to be used on aluminum or magnesium. It is extremely

expensive because of its silver content.

Thread-bcking Compounds

Some of the removable thread-locking compounds (such as

Loctite) also serve as antigalling and lubricating substances.

However, they are epoxies, which have a maximum operating

temperature of approximately 275 “F.

Corrosion

Galvanic Corrosion

Galvanic corrosion is setup when two dissimilar metals are

in the presence of an electrolyte, such as moisture. A galvanic

cell is created and the most active (anode) of the two materials

is eroded and deposited on the least active (cathode). Note that

the farther apart two materials are in the following list, the

greater the galvanic action between them.

According to reference 2 the galvanic ranking of some

common engineering materials is as follows:

(1) Magnesium (most active)

(2) Magnesium alloys

(3) Zinc

(4) Aluminum 5056

(5) Aluminum 5052

(6) Aluminum 1100

(7) Cadmium

(8) Aluminum 2024

(9) Aluminum 7075

(10) Mild steel

(11) Cast iron

(12) Ni-Resist

(13) Type 410 stainless (active)

(14) Type 304 stainless (active)

(15) Type 316 stainless (active)

(16) Lead

(17) Tin

(18) Muntz Metal

(19) Nickel (active)

Cswagelok Company, Solon,ohio.

(20)

(21)

(22)

(23)

(24)

(25)

(26)

(27)

(28)

(29)

(30)

(31)

(32)

(33)

(34)

(35)

(36)

Inconel (active)

Yellow brass

Admiralty brass

Aluminum brass

Red brass

Copper

Silicon bronze

70-30 Copper-nickel

Nickel (passive)

Inconel (passive)

Titanium

Monel

Type 304 stainless (passive)

Type 316 stainless (passive)

Silver

Graphite

Gold (least active)

Note the difference between active and passive 304 and 316

stainless steels. The difference here is that passivation of

stainless steels is done either by oxidizing in an air furnace

or treating the surface with an acid to cause an oxide to form.

This oxide surface is quite inert in both cases and deters

galvanic activity.

Because the anode is eroded in a galvanic cell, it should be

the larger mass in the cell. Therefore, it is poor design practice

to use carbon steel fasteners in a stainless steel or copper

assembly. Stainless steel fasteners can be used in carbon steel

assemblies, since the carbon steel mass is the anode.

Magnesium is frequently used in lightweight designs because

of its high strength to weight ratio. However, it must be totally

insulated from fasteners by an inert coating such as zinc

chromate primer to prevent extreme galvanic corrosion.

Cadmium- or zinc-plated fasteners are closest to magnesium

in the galvanic series and would be the most compatible if the

insulation coating were damaged.

Stress Corrosion

Stress corrosion occurs when a tensile-stressed part is placed

in a corrosive environment. An otherwise ductile part will fail

at a stress much lower than its yield strength because of surface

imperfections (usually pits or cracks) created by the corrosive

environment. In general, the higher the heat-treating temperature of the material (and tie lower the ductility), the more

susceptible it is to stress corrosion cracking.

The fastener material manufacturers have been forced to

develop alloys that are less sensitive to stress corrosion. Of

the stainless steels, A286 is the best fastener material for

aerospace usage. It is not susceptible to stress corrosion but

usually is produced only up to 160-ksi strength (220-ksi A286

fasteners are available on special order). The higher strength

stainless steel fasteners (180 to 220 ksi) are usually made of

17-7PH or 17-4PH, which are stress corrosion susceptible.

Fasteners made of superalloy suchasInconel718 or MP35N

are available if cost and schedule are not restricted.

5
An alternative is to use a high-strength carbon steel (such

as H- 11 tool steel with an ultimate tensile strength of 300 ksi)

and provide corrosion protection. However, it is preferable

to use more fasteners of the ordinary variety and strength, if

possible, than to use a few high-strength fasteners. Highstrength fasteners (greater than 180 ksi) bring on problems

such as brittleness, critical flaws, forged heads, cold rolling

of threads, and the necessity for stringent quality control

procedures. Quality control procedures such as x-ray, dye

penetrant, magnetic particle, thread radius, and head radius

inspections are commonly used for high-strength fasteners.

Hydrogen Embrittlement

Hydrogen embrittlement occurs whenever there is free

hydrogen in close association with the metal. Since most

plating processes are the electrolytic bath type, free hydrogen

is present. There arethree types ofhydrogen-metal problems:

(1) Hydrogen chemical reaction: Hydrogen reacts withthe

carbon in steel to form methane gas, which can lead to crack

development and strength reduction. Hydrogen can also react

with alloying elements such as titanium, niobium, or tantalum

to form hydrides. Because the hydrides are not as strong as

the parent alloy, they reduce the overall strength of the part.

(2) Internal hydrogen embrittlement: Hydrogen can remain

in solution interstitially (between lattices in the grain structure)

and can cause delayed failures afier proof testing. There is

no external indication that the hydrogen is present.

(3) Hydrogen environment embrittlement: This problem is

only present in a high-pressure hydrogen environment such

as a hydrogen storage tank. Unless a fastener was under stress

inside such a pressure vessel, this condition would not be

present,

Most plating specifications now state that a plated carbon

steel fastener “shall be baked for not less than 23 hours at

375 + 25 “F within 2 hours after plating to provide hydrogen

embrittlement relief” (per MIL-N–25027D). In the past the

plating specifications required baking at 375 & 25 “F for only

3 hours within 4 hours after plating. This treatment was found

to be inadequate, and most plating specifications were revised

in 198 1–82 to reflect the longer baking time. Hydrogen

embrittlement problems also increase as the fastener strength

increases.

Cadmium Embrittlement

Although hydrogen embrittlement failure of materials is well

documented (ref. 3), the effects of cadmium embrittlement are

not. In general, hydrogen embrittlement failure of cadmiumplated parts can start as low as 325 ‘F, but cadmium

embrittlement can start around 400 0F. Since both elements

are normally present in elevated-temperature failure of

cadmium-plated parts, the combined effect of the two can be

disastrous. However, the individual effect of each is

indeterminate.

Locking Methods

Tapped Holes

In a tapped hole the locking technique is normally on the

fastener. One notable exception is the Spiralock7 tap shown

in figure 1. The Spiralock thread form has a 30° wedge ramp

at its root. Under clamp load the crests of the male threads

are wedged tightly against the ramp. This makes lateral

movement, which causes loosening under vibration, nearly

impossible. Independent tests by some of the aerospace

companies have indicated that this type of thread is satisfactory

for moderate resistance to vibration, The bolt can have a

standard thread, since the tapped hole does all the locking.

Locknuts

There are various types of locking elements, with the

common principle being to bind (or wedge) the nut thread to

the bolt threads. Some of the more common locknuts are

covered here.

Split beam.–The split-beam locknut (fig. 2) has slots in the

top, and the thread diameter is undersized in the slotted

portion. The nut spins freely until the bolt threads get to the

slotted area. The split “beam” segments are deflected outward

by the bolt, and a friction load results from binding of the

mating threads.

Wedge ramps resist

transverse movement

Figure 1.–Spiralock thread.

mw

Full-height,

heavy-duty hex

Figure 2 ,—Split-beam locknut

7Distributed by Detroit Tap & Tool Company, Detroit, Michigan, through

license from H.D. Holmes.

6
e e.

Out-of-round Barrel returns to

@ ‘i:;:’+e’’ip’ica’shapeb

(a) (b) (c)

(a) Before assembly.

(b) Assembled.

(c) After withdrawal.

Figure 3.—Deformed-thread locknut.

Deiormed thread. -The deformed-thread locknut (fig. 3)

isa common locknut, particularly inthe aerospace industry.

Its advantages are as follows:

(1) The nut can be formed in one operation.

(2) The temperature range is limited only by the parent

metal, its plating, or both.

(3) The nut can be reused approximately 10 times before

it has to be discarded for loss of locking capability.

Nylok pellet. –The Nylok8 pellet (of nylon) is usually

installed in the nut threads as shown in figure 4. A pellet or

patch projects from the threads. When mating threads engage,

compression creates a counterforce that results in locking

contact. The main drawback of this pellet is that its maximum

operating temperature is approximately 250 “F. The nylon

pellet will also be damaged quickly by reassembly.

bcking collar and seal. —A fiber or nylon washer is

mounted in the top of the nut as shown in figure 5. The collar

has an interference fit such that it binds on the bolt threads.

It also provides some sealing action from gas and moisture

leakage. Once again the limiting feature of this nut is the

approximate 250 0F temperature limit of the locking collar.

A cost-saving method sometimes used instead of a collar

or nylon pellet is to bond a nylon patch on the threads of either

the nut or the bolt to get some locking action. This method

is also used on short thread lengths, where a drilled hole for

a locking pellet could cause severe stress concentration.

Caste12ated nut.—The castellated nut normally has six slots

as shown in figure 6(a). The bolt has a single hole tirough

its threaded end. The nut is torqued to its desired torque value.

It is then rotated forward or backward (depending on the user’s

sNylok Fastener Corporation, Rochester, Michigan.

~ Ny[ok pellet

*

If

~ Nut

Figure 4. —Nylok pellet locknut.

~ Collar

/

Figure 5 .—Locking collar,

~ Cotter

(a) (b)

(a) Slots.

(b) Cotter pin locking.

Figure 6. —Castellated nut.

preference) to the nearest slot that aligns with the drilled hole

in the bolt. A cotter pin is then installed to lock the nut in

place as shown in figure 6(b). This nut works extremely well

for low-torque applications such as holding a wheel bearing

in place.

Jam nuts. –These nuts are normally “jammed” together

as shown in figure 7, although the “experts” cannot agree

on which nut should be on the bottom. However, this type

of assembly is too unpredictable to be reliable. If the inner

nut is torqued tighter than the outer nut, the inner nut will yield

before the outer nut can pick up its full load. On the other

hand, if the outer nut is tightened more than the inner nut,

the inner nut unloads. Then the outer nut will yield before the

inner nut can pick up its full load. It would be rare to get the

correct amount of torque on each nut. A locknut is a much

more practical choice than a regular nut and a jam nut.

However, a jam nut can be used on a turnbuckle, where it

does not carry any of the tension load.

7
&

c Jam /

/ nut

Figure 7 ,—Jam nut.

u

(a)

Figure 8. —DurIock nut,

Serrated-face nut (or bolthead).-The serrated face of this

nut (shown in fig. 8) digs into the bearing surface during final

tightening. This means that it cannot be used with a washer

or on surfaces where scratches or corrosion could be a

problem.

According to SPS Technologies, their serrated-face bolts

(Durlock 180) require 110 percent of tightening torque to

loosen them. Their tests on these bolts have shown them to

have excellent vibration resistance.

Uckwiring. –Although Iockwiring is a laborious method

of preventing bolt or nut rotation, it is still used in critical

applications, particularly in the aerospace field, The nuts

usually have drilled corners, and the bolts either have

throughholes in the head or drilled corners to thread the

lockwire through. A typical bolthead lockwiring assembly is

shown in figure 9(a), and a typical nut lockwiring assembly

is shown in figure 9(b).

Easy

start

(b)

(a) Multiple fastener application (double-twist method, single hole).

(b) Castellated nuts on undrilled studs (double-twist method),

Figure 9. —Lockwiring.

Direct interfering thread.-A direct interfering thread has

an oversized root diameter that gives a slight interference fit

between the mating threads. It is commonly used on threaded

studs for semipermanent installations, rather than on bolts and

nuts, since the interference fit does damage the threads.

Tapered thread. –The tapered thread is a variation of the

direct interfering thread, but the difference is that the minor

diameter is tapered to interfere on the last three or four threads

of a nut or bolt as shown in figure 10.

Nutplates.—A nutplate (fig. 11) is normally used as a blind

nut.

m. ..-. ,,. . . . . . . . . .

1ney can De rlxea or rloatlng. in actalt]on, tney can nave

Locking

action

starts

Total

seal

and

locking

action

Figure 10,—Tapered thread,
(a) (b)

(a) Fixed.

(b) Floating.

Figure 11.—Nutplate

most of the locking and sealing features of a regular nut.

Nutplates are usually used on materials too thin to tap. They

are used primarily by the aerospace companies, since their

installation is expensive. At least three drilled holes and two

rivets are required for each nutplate installation.

kkrng Adhesives

Many manufacturers make locking adhesives (or epoxies)

for locking threads. Most major manufacturers make several

grades of locking adhesive, so that the frequency of

disassembly can be matched to the locking capability of the

adhesive. For example, Loctite 242 is for removable fasteners,

and Loctite 2719 is for tamperproof fasteners. Other

manufacturers such as Bostik, NDIndustries, Nylock, 3M, and

Permaloc make similar products.

Most of these adhesives work in one of two ways. They are

either a single mixture that hardens when it becomes a thin

layer in the absence of air or an epoxy in two layers that does

not harden until it is mixed and compressed between the mating

threads. Note that the two-layer adhesives are usually put on

the fastener as a‘ ‘ribbon” or ring by the manufacturer. These

ribbons or rings do have some shelf life, as long as they are

not inadvertently mixed or damaged.

These adhesives are usually effective as thread sealers as

well. However, none of them will take high temperatures. The

best adhesives will function at 450 “F; the worst ones will

function at only 200 “F.

Washers

Belleville Washers

Belleville washers (fig. 12) are conical washers used more

for maintaining a uniform tension load on a bolt than for

locking. If they are not completely flattened out, they serve

as a spring in the bolt joint. However, unless they have

serrations on their surfaces, they have no significant locking

capability. Of course, the serrations will damage the mating

surfaces under them. These washers can be stacked in

Shctite Corporation, Newington, Connecticut.

combinations as shown in figure 13 to either increase the total

spring length (figs. 13(a) and (c)) or increase the spring

constant (fig. 13(b)).

Wkwashers

The typical helical spring washer shown in figure 14 is made

of slightly trapezoidal wire formed into a helix of one coil so

that the free height is approximately twice the thickness of the

washer cross section. They are usually made of hardened

carbon steel, but they are also available in aluminum, silicon,

brome, phosphor-bronze, stainless steel, and K-Monel.

The lockwasher serves as a spring while the bolt is being

tightened. However, the washer is normally flat by the time

the bolt is fully torqued. At this time it is equivalent to a solid

flat washer, and its locking ability is nonexistent. In summary,

a Iockwasher of this type is useless for locking.

I

(a) Smooth.

(b) Serrated.

Figure 12.—Types of BelIevilIe washers.
(a)

(b)

(c)

(a) In series.

(b) In parallel.

(c) In-parallel series.

Figure 13.—Combinations of Belleville washers.

Figure 14.—Helical spring washers.

Tooth (or Star) Lockwashers

Tooth Iockwashers (fig, 15) are used with screws and nuts

for some spring action but mostly for locking action. The teeth

are formed in a twisted configuration with sharp edges. One

edge bites into the boltbead (or nut) while the other edge bites

into the mating surface. Although this washer does provide

some locking action, it damages the mating surfaces. These

scratches can cause crack formation in highly stressed

fasteners, in mating parts, or both, as well as increased

corrosion susceptibility.

Self-Aligning Washers

(a) (b)

(a) Flat,

(b) Countersunk.

Figure 15.—Tooth Iockwashers.

~ 8“ maximum misalignment of nut and

bearing sudace at assembly

Figure 16.—Self-aligning nut.

Inserts

An insert is a special type of device that is threaded on its

inside diameter and locked with threads or protrusions on its

outside diameter in a drilled, molded, or tapped hole. It is used

to provide a strong, wear-resistant tapped hole in a sofi material

such as plastic and nonferrous materials, as well as to repair

stripped threads in a tapped hole.

The aerospace industry uses inserts in tapped holes in soft

materials in order to utilize small high-strength fasteners to

save weight. The bigger external thread of the insert (nominally

1/8 in. bigger in diameter than the internal thread) gives, for

example, a 10-32 bolt in an equivalent 5/16– 18 nut.

In general, there are two types of inserts: those that are

threaded externally, and those that are locked by some method

other than threads (knurls, serrations, grooves, or interference

fit). Within the threaded inserts there are three types: the wire

thread, the self-tapping, and the solid bushing.

A self-aligning washer is used with a mating nut that has Threaded Inserts

conical faces as shown in figure 16. Because there is both a

weight penalty and a severe cost penalty for using this nut, Wire threud.-The wire thread type of insert (Heli-coil 1°)

it should be used only as a last resort. Maintaining parallel

mating surfaces within acceptable limits (20 per SAEHandbook 10E~hartFastening Systems Group, Heli-Coil Division, Danbury,

(ref. 4)) is normally the better alternative. Connecticut.
I 1

(a) (b)

Figure 17.—Wire thread insert installation.

/

-Tang7

\

\

*

Deformed

coil

(a) (b)

(a) Free running.

(b) Locking.

Figure 18.—Wire thread insert types.

is a precision coil of diamond-shaped CRESwire that forms

both external and internal threads as shown in figure 17. The

coil is made slightly oversize so that it will have an interference

fit in the tapped hole. In addition, this insert is available with

a deformed coil (fig. 18) for additional locking. The tang is

broken off at the notch after installation.

The wire thread insert is the most popular type for repair

of a tapped hole with stripped threads, since it requires the

least amount of hole enlargement. However, the solid bushing

insert is preferred if space permits.

Self-tapping. –Most of the self-tapping inserts are the solid

bushing type made with a tapered external thread similar to

a self-tapping screw (fig. 19). There are several different

(a) Slotted.

(b) Nylok.

Figure 19.—Self-tapping inserts.

locking combinations, such as the Nylok plug (fig. 19(b)) or

the thread-forming Speedsertll deformed thread (fig. 20). An

additional advantage of the thread-forming insert is that it

generates no cutting chips, since it does not cut the threads.

However, it can only be used in softer materials.

-

\

t

i)

t

I E“

e——=—

I F\ / !

I

1

Figure 20. —Speedsert.

11Rexnord s~ialty Fasteners Division, Torrance, California.

11
Solid bushing. -Solid bushing inserts have conventional

threads both internally and externally. Apopulartype is the

Keensert 11shown in figure 21. The locking keys are driven

in after the insert is in place. Another manufacturer uses a

two-prong ring for locking. These inserts are also available

with distorted external thread or Nylok plugs for locking.

Nonthreaded Inserts

Pbstic expandable. —The most fmiliar of the nonthreaded

inserts is the plastic expandable type shown in figure 22. This

insert has barbs on the outside and longitudinal slits that allow

it to expand outward as the threaded fastener is installed,

pushing the barbs into the wall of the drilled hole. (See ref. 5.)

Molded in place. –This type of insert (fig. 23) is knurled

or serrated to resist both pullout and rotation. It is commonly

used with ceramics, rubber, and plastics, since it can develop

higher resistance to both pullout and rotation in these materials

than self-tapping or conventionally threaded inserts. (See

ref. 5.)

Ultrasonic.-UItrasonic inserts (fig. 24) have grooves in

various directions to give them locking strength. They are

installed in a prepared hole by pushing them in while they are

being ultrasonically vibrated. The ultrasonic vibration melts

the wall of the hole locally so that the insert grooves are

“welded” in place. Since the area melted is small, these inserts

do not have the holding power of those that are molded in

place. Ultrasonic inserts are limited to use in thermoplastics.

(See ref. 5.)

Figure 21 .—Keensert.

Figure 22 ,—Plastic expandable insert.

B

e

*“3:.:.’

. . ..

.. .

, “:.“.-

.....

Figure 23 .—Molded-in-place insert.

Figure 24.—Ultrasonic inserts.

Threads

Types of Threads

Since complete information on most threads can be found

in the ANSI standards (ref. 6), the SAEHandbook (ref. 4), and

the National Institute of Standards and Technology (formerly

the National Bureau of Standards) Handbook H-28 (ref. 7)

no thread standards will be included in this handbook. The

goal here is to explain the common thread types, along with

their advantages and disadvantages. The common thread types

are unified national coarse (UNC), unified national fine (UNF),

unified national extra fine (UNEF), UNJC, UNJF, UNR, UNK,

and constant-pitch threads.

Unified natzonal coarse. –uNc is the most commonly used

thread on general-purpose fasteners. Coarse threads are deeper

than fine threads and are easier to assemble without cross

threading. The manufacturing tolerances can be larger than

for finer threads, allowing for higher plating tolerances. UNC

threads are normally easier to remove when corroded, owing

to their sloppy fit. However, a UNC fastener can be procured

with a class 3 (tighter) fit if needed (classes to be covered later).

Unified national fine. —UNF thread has a larger minor

diameter than UNC thread, which gives UNFfasteners slightly

higher load-carrying and better torque-locking capabilities than

UNC fasteners of the same identical material and outside

diameter. The fine threads have tighter manufacturing

tolerances than UNC threads, and the smaller lead angle allows

for finer tension adjustment. UNF threads are the most widely

used threads in the aerospace industry.

Unified n&.On~ eXtra fine. -uNEF iS a still finer type of

thread than UNF and is common to the aerospace field. This

thread is particularly advantageous for tapped holes in hard

materials and for thin threaded walls, as well as for tapped

holes in thin materials.

12
UNJC and UNJF threads. —‘‘J” threads are made in both

external and internal forms. The external thread has a much

larger root radius than the corresponding UNC, UNR, UNK, or

UNF threads. This radius is mandatory and its inspection is

required, whereas no root radius is required on UNC, UNF,

or UNEF threads. Since the larger root radius increases the

minor diameter, a UNJFor UNJC fastener has a larger net tensile

area than a corresponding UNF or UNC fastener. This root

radius also gives a smaller stress concentration factor in the

threaded section, Therefore, high-strength (> 180 ksi) bolts

usually have “J” threads.

UNR threads.—The UNR external thread is a rolled UN

thread in all respects except that the root radius must be

rounded. However, the root radius and the minor diameter

are not checked or tolerance. There is no internal UNRthread.

UNK threads. —The UNKexternal threads are similar to UNR

threads, except that tie root radius and the minor diameter

are tolerance and inspected. There is no internal UNKthread.

According to a survey of manufacturers conducted by the

Industrial Fasteners Institute, nearly all manufacturers of

externally threaded fasteners make UNRrolled threads rather

than plain UN. The only exception is for ground or cut threads.

Constant-pitch threads. —These threads offer a selection of

pitches that can be matched with various diameters to fit a

particular design. This is a common practice for bolts of l-in.

diameter and above, with the pitches of 8, 12, or 16 threads

per inch being the most common.

A graphical and tabular explanation of UN, UNR, UNK, and

UNJ threads is given on page M–6 of reference 8. A copy

(fig. 25) is enclosed here for reference.

Classes of Threads

Thread classes are distinguished from each other by the

amounts of tolerance and allowance. The designations run from

1A to 3A and lB to 3B for external and internal threads,

respectively. A class 1 is a looser fitting, general-purpose

thread; a class 3 is the closer-toleranced aerospace standard

thread. (The individual tolerances and sizes for the various

classes are given in the SAE Handbook (ref 4).)

Forming of Threads

Threads may be cut, hot rolled, or cold rolled. The most

common manufacturing method is to cold form both the head

and the threads for bolts up to 1 in. in diameter. For bolts

above 1-in. diameter and high-strength smaller bolts, the heads

are hot forged. The threads are still cold rolled until the bolt

size prohibits the material displacement necessary to form the

threads (up to a constant pitch of eight threads per inch).

Threads are cut only at assembly with taps and dies or by lathe

cutting.

Cold rolling has the additional advantage of increasing the

strength of the bolt threads through the high compressive

surface stresses, similar to the effects of shot peening. This

process makes the threads more resistant to fatigue cracking.

Fatigue-Resistant Bolts

If a bolt is cycled in tension, it will normally break near

the end of the threaded portion because this is the area of

maximum stress concentration. In order to lessen the stress

concentration factor, the bolt shank can be machined down

to the root diameter of the threads. Then it will survive tensile

cyclic loading much longer than a standard bolt with the shank

diameter equal to the thread outside diameter.

Fatigue (Cyclic) Loading of Bolts

The bolted joint in figure 26 (from ref. 9) is preloaded with

an initial load Fi, which equals the clamping load FC,before

the external load Fe is applied. The equation (from ref. 11)

for this assembly is

()K~

F~=Fi+ — F,

K~+ KC

where Fb is the total bolt load. In this equation Kb is the

spring constant of the bolt and KCis the spring constant of the

clamped faces. To see the effects of the relative spring

constants, let R = KC/Kb. Then (from ref. 10)

Fb=Fi+ ()1

— F,

,l+R

In a normal clamped joint KC is much larger than Kb

(R = 5.0 for steel bolt and flanges), so that the bolt load does

not increase much as the initial external load Fc is applied.

(Note that the bolt load does not increase significantly until

Fe exceeds Fi.)

In order to further clarify the effect of externally applied

loads, a series of triangular diagrams (fig. 27, from ref. 11)

can be used to illustrate loading conditions.

Triangle OAB is identical in all four diagrams. The slope

of OA represents the bolt stiffness; the slope of AB represents

the joint stiffness ~oint is stiffer than bolt by ratio OC/CB.)

In figure 27(a) the externally applied load F,(a) does not

load the bolt to its yield point. In figure 27@) the bolt is loaded

by Fe(b) to its yield point, with the corresponding decrease

in clamping load to FCL,In figure 27(c) external load F,(c)

has caused the bolt to take a permanent elongation such that

the clamping force will be less than Fi when F,(c) is

removed. In figure 27(d) the joint has completely separated

on its way to bolt failure.

Note that the flatter the slope of OA (or the larger the ratio

OC/OB becomes), the smaller the effect F, has on bolt load.

Therefore, using more smaller-diameter fasteners rather than

a few large-diameter fasteners will give a more fatigue-resistant

joint.

Referring to figure 27(a), note that the cyclic (alternating)

load is that portion above Fi. This is the alternating load

13
60” SCREW THREAD NOMINAL FORMS (SEE ANSI STANDARDS FOR FURTHER DETAILS)

\\\\\\\\’~ UN INTERNAL ‘ ‘ “ THREAD

h\k @OOT TO CLCAQ O125D WIOTW-=.OG. .

Y’”

w C2.01 7., -,

0

5U

I

-1

W READ

ENllFICAllON

ANSI 1

STANDARDS

DOCUMENT5

~ERNAL

ROOT

EklERNAL

MINOR

DIAMETER

EKrERNAL

~READS

INTERNAL

THREADS

ANGLE AND

LEAD

TO IERANCE

UN THREADS

In$ernol and tie,nal

Jn!fied Screw Threod!

31 l–1960SeePogc

u–7! Metr, c Tro”sl atton

BI Io-1968

Gages ond Gagtng for

Un,f, ed Screw Threads

31 2-1966

External Thread Root

moy be Flot or

Rounded

External Thread M$nor

D,ame~e( *S not

tolecon.ed

UN Class,, I A 2A

ond 3A

UN Classes lB, 2B

o“d 36

Incu.lduolly Eqaovole”I

to 50t.01 P D Toleronc,

Checked CI”ly when

Specl(ed

UNR THREADS

Eaier..l Oniy

Jn!f!ed Screw Threads

BI 1-1960 See Page

W71 Me!r!c Translot, or

B1 .10–1968 ,Draft!

UNR Addend. m to

BI.1–1960 ISee Page

M–191

Gages ond Gogtng for

Un,f, ed Screw Threads

81.2-1966

Ex!ernai Thread Root

Rad, us Rq. tred

External Thread M$nor

D(ame!er ,, no)

Tole<ancvd

UNR Classes 1 A, 2A

and 3A

No In!ernol Threods

Des,gna!ec! UNR

UN RM.tes w,th UN

Intern. ) Thread

Indiv, duolly Equ(vale”I

10 50’< 01 P D Toleronc,

Checked only -hen

Spec)l!ed

7

UNK TMREAL)S I UNJ lHREADS

Iii.rnoi Only { Infernal and Eder”ol

Draft: B1 15 for Form

,Druftl 81 14 Ior Form ond Con!orma”ce No

and Con(ocma”ce Rad, us Requ, reti on

Internal Threod,

Exter. ol Threod Root E.te, nal Thread Root

Rod,., Monda!o<y RadI. s Mandatory

Check Req., red Check Requ~(ed

UNK Clo>>e> 2A

UNJ Class 3A Motes

and 3A

only w,th UNJ Internol

Thread,

No Internol Threads

Destg..ted UNK

UNJ Closses 3e and

3BG No Rod,. >

Requ, red on I“ternol

Moles -Ith UN or UNJ Th(eod

Internal Thread

I“tii., duolly Equ Ivolem I“di., dually Equlvolc.

to 40% of P D Tole, on<, ,0 40: ~f P D Toler. nc

Mandatory Check Moodolo, y Check

Requ, red Req., ted

NOTES: 1 Refer to the aoorooc! ate Slanda,ds. as lIsId !or com

ole!e thread deta)ls am coclormdnce dat. The ao

fOr con,olere dela,ls a~ dala, and fakes ~,ecede~ce

over lh, s sheet

oroorna!e CurIeflt Standard IS :he authuraral, ve docun!ent 2 These StArdards may be ohta nd Inrouqt fiS~~E

Figure 25.—Explanation of UN, UNR, UNK, and UNJ threads. (From ref. 8.) Reprinted with permission of Industrial Fasteners Institute.

14
~

Fe

(a) (b)

(a) Bolted flanges with external load.

(b) Free body with no external load,

(c) Free body with external load.

Fb

\

r

J

Fe

(c)

Figure 26.–Fatigue loading of bolts.

I Ultimate bolt load line

r-u

u’ ~ Bolt preioad line

~ FY I

Yield bolt load line

=

I

2 \*

/ 1

Cyclic load AA F, A

- Fe(c)

o c BO CBQ CBO

Elongation /

f. Joint

(a) (b) (c) (d) separation

Figure 27. —Bott external loading.

(stress) to be used on a stress-versus-load-cycles diagram of

the bolt material to predict the fatigue life of the bolts. Note

that an initial preload Fi near the bolt yields minimizes cyclic

loading.

Thermal Cyclic Loading of Bolts

If the bolt and joint are of different materials, an operating

temperature higher or lower than the installation temperature

can cause problems. Differential contraction can cause the joint

to unload (or separate); differential expansion can cause

overloading of the fasteners. In these cases it is common

practice to use conical washers (see washer section of this

manual) to give additional adjustments in fastener and joint

loading.

Fastener Torque

Determining the proper torque for a fastener is tie biggest

problem in fastener installation. Some of tie many variables

causing problems are

(1)

(2)

(3)

(4)

(5)

(6)

The coefficient of friction between mating threads

The coefficient of friction between the bolthead (or nut)

and its mating surface

The effect of bolt coatings and lubricants on the friction

coefficients

The percentage of bolt tensile strength to be used for

preload

Once agreement is reached on item 4, how to accurately

determine this value

Relative spring rates of the structure and the bolts

15
—

—

—

—

::: :::: ::.

:::: ,.:

:::: :: :,. : :::

::::

:::

:::: ::
(7) Interaction formulas to be used for combining simultaneous shear and tension loads on a bolt (Should

friction loads due to bolt clamping action be included

in the interaction calculations?)

(8) Whether’’running torque’’ foralocking device should

be added to the normal torque

Development of Torque Tables

The coefficient of friction can vary from 0.04 to 1.10,

depending on the materials and the lubricants being used

between mating materials. (Table IV from ref. 12 gives a

variety of friction coefficients.) Since calculated torque values

are a function of the friction coefficients between mating

threads and between the bolthead or nut and its mating surface,

it is vitally important that the torque table values used are

adjusted to reflect any differences in friction coefficients

between those used to calculate the table and the user’s values.

Running torque should be included in the values listed in the

tables because any torque puts shear load on the bolt.

.The torque values in table V have been calculated as noted

in the footnotes, by using formulas from reference 13. (A

similar table was published in Product Engineering by Arthur

Kern around 1944.)

Higher torques (up to theoretical yield) are sometimes used

for bolts that cannot be locked to resist vibration. The higher

load will increase the vibration resistance of the bolt, but the

bolt will yield and unload if its yield point is inadvertently

exceeded. Since the exact yield torque cannot be determined

without extensive instrumentation, it is not advisable to torque

close to the bolt yield point.

Fastener proof load is sometimes listed in the literature. This

value is usually 75 percent of theoretical yield, to prevent

inadvertent yielding of the fastener through torque

measurement inaccuracies.

Alternative Torque Formula

A popular formula for quick bolt torque calculations is

T = KFd, where T denotes torque, F denotes axial load, d

denotes bolt diameter, and K(torque coefficient) is a calculated

value from the formula:

() K= & tan~+psecu

+ 0.625PC

2d l–p tan ~ sec a

as given in reference 14 (p. 378) where

d. thread mean diameter

$ thread helix angle

P friction coefficient between threads

a’ thread angle

P< friction coefficient between bolthead (or nut) and

clamping surface

The commonly assumed value for K is 0.2, but this value

should not be used blindly. Table VI gives some calculated

values of K for various friction coefficients. A more realistic

“typical” value for K would be 0.15 for steel on steel. Note

that p and PCare not necessarily equal, although equal values

were used for the calculated values in table VI.

Torque-Measuring Methods

A number of torque-measuring methods exist, starting with

the mechanic’s “feel” and ending with installing strain gages

on the bolt. The accuracy in determining the applied torque

values is cost dependent. Tables VII and VIII are by two

different “experts,” and their numbers vary. However, they

both show the same trends of cost versus torque accuracy.

Design Criteria

Finding Shear Loads on Fastener Group

When the load on a fastener group is eccentric, the first task

is to find the centroid of the group. In many cases the pattern

will be symmetrical, as shown in figure 28. The next step is

to divide the load R by the number of fasteners n to get the

~~rect shear load PC(fig. 29(a)). Next, find ~rj for the group

of fasteners, where rn is the radial distance of each fastener

from the centroid of the group. Now calculate the moment

about the centroid (M = Re from fig. 28). The contributing

shear load for a particular fastener due to the moment can be

found by the formula

where r is the distance (in inches) from the centroid to the

fastener in question (usually the outermost one). Note that this

is analogous to the torsion formula, ~ = Tr/J, except that P.

is in pounds instead of stress. The two loads (PCand Pe) can

now be added vectorally as shown in figure 29(c) to get the

resultant shear load P (in pounds) on each fastener. Note that

the fastener areas are all the same here. If they are unequal,

the areas must be weighted for determining the centroid of

the pattern.

Further information on this subject may be found in

references 16 and 17.

Finding Tension Loads on Fastener Group

This procedure is similar to the shear load determination,

except that the centroid of the fastener group may not be the

geometric centroid. This method is illustrated by the bolted

bracket shown in figure 30.

The pattern of eight fasteners is symmetrical, so that the

tension load per fastener from P, will be Pi/8, The additional
TABLE V.–BOLT TORQUE

[No lubrication on threads. Torque values are

based on friction coefficients of 0.12 between

threads and 0.14 between nut and washer or

head and washer, as manufactured (no special

cleaning). ]

Size

10-24

10-32

1A-20

%-4–28

51]6–18

‘1,6–24

Y8–16

‘h-24

‘/,6–14

7/,6–20

[A–13

Y2–20

9/,6-12

91,C-18

70-11

?8–18

%-lo

Y4-16

T8‘9

78-14

1-8

1-14

l~_7

1%-12

]~_7

l’h-12

Root area,

in.2

0,0145

.0175

.0269

.0326

.0454

.0524

.0678

.0809

.0903

.1090

.1257

.1486

.1620

.1888

.2018

.240il

.3020

.3513

.4193

,4805

,5510

.6464

,6931

,8118

.8898

1.0238

Torque range

(class8, 150ksi,

bolts a)

23 to 34 in.-lb

29t043 in.-lb

54t081 in.-lb

68to 102in.-lb

l17to 176in, -lb

139to 208 in-lb

205 to 308 in-lb

230t0345 in.-lb

28 to42 fi-lb

33 to 50 fi-lb

42 to64 ft-lb

52t077 R-1b

61 to91 ft-lb

73to 109 ft-lb

84to 126 ft-lb

104to 156 ft-lb

1117 to 176 ft-lb

>139 to 208 ft-lb

J184 to 276 ft-lb

’213 to 320 ft-lb

1276 to 414 ft-lb

’323 to 485 ft-lb

~390 to 585 ft-lb

’465 to 698 ft-lb

’559 to 838 ft-lb

~655 to 982 ft-lb

aThe value~ e,. cn arc50 and 75 Dercent ofthcoretlcal v~eld

strength ofa bolt material with ay,eld “f 120 ksl. Corresponding values for matertals with dlfie rent y Ield strength,

can be obtained by muhlply~ng tbesc table values by che rat~o

of the respective rndterlal yield strengths.

bBolt, ~ro 75.i”, diameter and larger have reduced allO~-

ables (75 ~rcent of normal strength) owtng to in. bd!ty

t. hcattrcat [his Iargc across section t<>an even hardness.

Repr,ntcd from Mach,ne Design, Nob 19, 1987 Copyright, 1987 by Penton Publ,sblng, Inc

Cleveland. OH.

TABLE VI.–TORQUE COEFFICIENTS

Friction coefficient Torque

Between

threads,

P

0.05

,10

.15

.20

coefticienl

Between K

bolthead

(or nut)

and clamping

surface,

P.

0.05 0.074

.10 .133

.15 .189

.20 .250

TABLE VII.–INDUSTRIAL FASTENERS

INSTITUTE’S TORQUE-MEASURING METHOD

[From ref. 8.]

Preload measuring method

Feel (operator’s judgment)

Torque wrench

Turn of the nut

had-indicating washers

Fastener elongation

Strain gages

Accuracy,

percent

*35

*25

+ 15

* 10

*3t05

*1

Relative cos

1

1.5

3

7

15

20

moment P2h will also produce a tensile load on some

fasteners, but the problem is to determine the “neutral axis”

line where the bracket will go from tension to compression.

If the plate is thick enough to take the entire moment Z’2hin

bending at the edge AB, that line could be used as the heeling

point, or neutral axis. However, in this case, I have taken the

conservative approach that the plate will not take the bending

and will heel at the line CD. Now the ~r~ will only include

bolts 3 to 8, and the r~’s (in inches) will be measured from

line CD. Bolts 7 and 8 will have the highest tensile loads (in

pounds), which will be P = P~ + PM, where P~ = P, /8 and

Mr P2hr7

Pm=—=—

Zrj Xr;

An alternative way of stating this relationship is that the bolt

load is proportional to its distance from the pivot axis and the

moment reacted is proportional to the sum of the squares of

the respective fastener distances from the pivot axis.

At this point the applied total tensile load should be compared

with the total tensile load due to fastener torque. The torque

should be high enough to exceed the maximum applied tensile

load in order to avoid joint loosening or leaking. If the bracket

geometry is such that its bending capability cannot be readily

determined, a finite element analysis of the bracket itself may

be required.

Combining Shear and Tensile Fastener Loads

When a fastener is subjected to both tensile and shear loading

simultaneously, the combined load must be compared with the

total strength of the fastener, Load ratios and interaction curves

are used to make this comparison. The load ratios are

Actual shear load

R~(or RI) =

Allowable shear load

Actual tensile load

Rr(or R2) =

Allowable tensile load

18
TABLEVIII.–MACHINE DESIGN’STORQUE-MEASURINGMETHOD

[From ref. 15.]

(a) Typical tool accuracies

Type of Element Typical

tool controlled accuracy range,

percent of

full scale

Slug wrench Turn 1 Flat

Bar torque wrench Torque *3 to 15

Turn 1/4 Flat

[mpact wrench Torque *10 to 30

Turn *lo to 20°

Hydraulic wrench Torque *3 to *lo

Turn *5 to 10°

Gearhead air- Torque *1O to *2O

powered wrench Turn *5 to 10°

Mechanical Torque f5 to 20

multiplier Turn *2 to 10”

Worm-gear torque Torque +0.25 to 5

wrench Turn *1 to5°

Digital torque Torque *1/4tol

wrench Turn 114 Flat

Ultrasonically Bolt elongation *l tolo

controlled wrench

Hydraulic tensioner Initial bolt *lto5

stretch

Computer-controlled Simultaneous +0.5 to 2

tensioning torque and turn

(b) Control accuracies

Element Preload accuracy, To maximize accuracy

controlled percent

rorque *15 to *3O Control bolt, nut, and washer hardness,

dimensions, and finish. Have consistent

hrbricant conditions, quantities, application, and types.

rum *15 to *3O Use consistent snug torque. Control part

gwmetry and finish. Use new snckets

and fresh lubes.

rorque and turn *1O to +25 Plot torque vs turn and compare to previously derived set of curves. Control

bolt hardness, finish, and geometry.

rorque past yield *3 to *lo Use “soft” bolts and tighten well past

yieId point. Use consistent snugging

torque. Control bolt hardness and

dimensons.

Bolt stretch +lto+8 Use bolts with flat, parallel ends. Leave

transducer engaged during tightening

operation. Mount transducer on bolt

centerline.

19
,

\

o

/

o

0 01

R

Figure 28.—Symmetrical load pattern.

Figure 29.—Combining of shear and moment loading.

The interaction curves of figure31 area series of curves with

their corresponding empirical equations. The most

conservative is R] + R2 = 1 and tie least conservative is

R; + R; = 1. This series of curves is from an old edition of

MIL-HDBK-5. It has been replaced by a single formula,

R; + R$ = 1, in the latest edition (ref. 18). However, it is

better to use RT + Rs = 1 if the design can be conservative

with respect to weight and stress.

Note that the interaction curves do not take into consideration

the friction loads from the clamped surfaces in arriving at bolt

shear loads. In some cases the friction load could reduce the

bolt shear load substantially.

Shear, R~ (or R,)

Figure 3 1.—Interaction curves.

B

D

o+2

0+4 0+6 0+8

PI

@+ I

A c ~n

tP1 PM

T

P2 ~

l\

h

tP~

I I I I

I 1

up- I

I I

I

I I )

Figure 30.—Bolted bracket,

20
The margin of safety 12 for a fastener from figure 31 is

MS =

1

–1

R; + R;

depending on which curve is used. However, note that

Rj + R;< 1 is a requirement for a positive margin of safety.

This formula also illustrates why high torque should not be

applied to a bolt when the dominant load is shear.

The margin of safety is calculated for borh yield and ultimate

material allowable, with the most critical value controlling

the design. A material with a low yield will be critical for yield

stress, and a material with a high yield will normally be critical

for ultimate stress.

Calculating Pullout Load for Threaded Hole

In many cases a bolt of one material may be installed in a

tapp~ hole in a different (and frequently lower strength)

material. If the full strength of the bolt is required, the depth

of the tapped hole must be determined for the weaker material

by using the formula

where

P

d.

F,

L

pullout load, lb

mean diameter of threaded hole, in. ( = pitch diameter

of threads)

material ultimate or yield shear stress

length of thread engagement, in.

The % factor is empirical. If the threads were perfectly

mated, this factor would be %, since the total cylindrical shell

area of the hole would be split equally between the bolt threads

and the tapped hole threads. The Y3 is used to allow for

mismatch between threads.

Further information on required tapped hole lengths is given

in reference 19.

Calculating Shank Diameter for “Number” Fastener

The shank diameter for a “number” fastener is calculated

from

Diameter = 0.060 + 0.013 N

lZMargin of safety is defined as

Allowable load (Stress)

–1

Actual load (Stress) x Safety factor

where N is the number (4, 6, 8, 10, 12) of the fastener. For

example, the shank diameter of a no. 8 fastener is

Diameter = 0.060 + 0.013(8) = 0.164 in.

Fastener Groups in Bearing (Shear Loading)

Whenever possible, bolts in shear should have a higher shear

strength than the bearing yield strength of the materials they

go through. Since the bolts have some clearance and position

tolerances in their respective holes, the sheet material must

yield in bearing to allow the bolt pattern to load all of the bolts

equally at a given location in the pattern. Note that the sloppier

the hole locations, the more an individual bolt must carry

before the load is distributed over the pattern.

Bolts and rivets should not be used together to carry a load,

since the rivets are usually installed with an interference fit.

Thus, the rivets will carry all of the load until the sheet or

the rivets yield enough for the bolts to pickup some load, This

policy also applies to bolts and dowel pins (or roll pins) in

a pattern, since these pins also have interference fits.

Fastener Edge Distance and Spacing

Common design practice is to use a nominal edge distance

-f 2D from the fastener hole centerline, where D is the fastener

diameter. The minimum edge distance should not be less than

1.5D. The nominal distance between fasteners is 4D, but the

thickness of the materials being joined can be a significant

factor. For thin materials, buckling between fasteners can be

a problem. A wider spacing can be used on thicker sheets,

as long as sealing of surfaces between fasteners is not a

problem.

Approximate Bearing and Shear Allowable

In the absence of specific shear and bearing allowable for

materials, the following approximations may be used:

Alloy and carbon steels: F,U = 0.6 F,U

Stainless steels: F,U = 0.55 F,.

where F$Uis ultimate shear stress and F[Uis ultimate tensile

stress. Since bearing stress allowable are empirical to begin

with, the bearing allowable for any given metallic alloy may

be approximated as follows:

FbU= 1.5 F,U

FbY= 1.5 Ffy

where FbU is ultimate bearing stress,

stress, and F. is tensile yield stress.

Fby is yield bearing

21
Proper Fastener Geometry Counterfeit Fasteners

Most military standard (MS)and national aerospace standard

(NAS) fasteners have coded callouts that tell the diameter, grip

length, drilling of the head or shank, and the material (where

the fastener is available in more than one material). Rather

than listing a group of definitions, it is easier to use the

NAS 1003 to NAS 1020 (fig. 32) as an example to point out

the following:

(1) The last two digits give the fastener diameter in

sixteenths of an inch.

(2) The first dash number is the grip length in sixteenths

of an inch.

(3) The letters given with the dash number indicate the head

and/or shank drilling.

In addition, an identifying letter or dash number is added to

indicate the fastener material. However, this systematic

practice is not rigidly followed in all MS and NAS fastener

standards.

Shear Heads and Nuts

In the aerospace industry the general ground rule is to design

such that fasteners are primarily in shear rather than tension.

As a result, many boltheads and nuts are made about one-half

as thick as normal to save weight. These bolts and nuts are

referred to as shear bolts and shear nuts, and care must be

used in never specifying them for tension applications. The

torque table values must also be reduced to one-half for these

bolts and nuts.

Use of Proper Grip Length

Standard design practice is to choose a grip length such that

the threads are never in bearing (shear), Where an exact grip

length is not available, the thickness of the washers used under

the nut or bolthead can be varied enough to allow proper grip.

Bolthead and Screwhead Styles

Although the difference between bolts and screws is not

clearly defined by industry, at least the head styles are fairly

well defined. The only discrepancy found in figure 33 is that

the plain head, with a square shoulder, is more commonly

called a carriage bolthead. The angle of countersunk heads

(flat) can vary from 60° to 120°, but the common values are

82° and 100”.

In the past two years a great deal of concern and publicity

about counterfeit fasteners has surfaced. The counterfeit case

with the most documentation is the deliberate marking of

grade 8.2 boron bolts as grade 8 bolts.

Grade 8.2 bolts are a low-carbon (0,22 percent C) boron

alloy steel that can be heat treated to the same roomtemperature hardness as grade 8 medium-carbon (O.37 percent C) steel. However, the room- and elevated-temperature

strengths of the grade 8.2 bolts drop drastically if they are

exposed to temperatures above 500 0F. Grade 8 bolts can be

used to 800 ‘F with little loss of room-temperature strength.

Other fasteners marked as MS and NAS but not up to the

respective MSor NASspecification have shown up; however,

documentation is not readily available. Since these fasteners

are imported and have no manufacturer’s identification mark

on them, it is not possible to trace them back to the guilty

manufacturer, U.S. Customs inspections have not been

effective in intercepting counterfeit fasteners.

Another problem with fasteners has been the substitution

of zinc coating for cadmium coating. If a dye is used with the

zinc, the only way to detect the difference in coatings is by

chemical testing.

Federal legislation to establish control of fastener materials

from the material producer to the consumer is being

formulated.

Bolthead Identification

Identifying an existing non-Ms, non-NAs, or non-Air ForceNavy bolt is usually a problem. Each manufacturer seems to

have a different system. Frank Akstens of Fastener Technology

International magazine (ref. 20) has compiled a good listing

of several hundred “common” bolts. His entire compilation

is enclosed as appendix A of this report. An international guide

to bolt manufacturer’s identification symbols has also been

published by Fastener Technology International magazine.

Fastener Strength

Allowable strengths for many types of fasteners are given

in MIL–HDBK–5 (ref. 18). Ultimate shear and tensile

strengths of various threaded fasteners are given in

appendix B of this report.
NATIONAL AEROSPACE STANDARD

~~~~~ l?60U$l*lCs A= IATION Or AMERICA INC ,725 OE SALES S7RCC’f N w WASHINGTON D C 20036 ——

D

POINT TO BE FLAT

ANO CHAMFEREO,

LENGTH OF POINT

TO FIRST COMPLETE

15 WI{EN SPECIFIED ‘HREAD - u ‘Ax

ROLLED THREAD MI L-S-8879 I’OLLOWIN(;

~LL K ~EU SPECIFI ED.

WW WRP EWES

‘“T’ONAL %>>ara.?

@ @

SASK

1

7URUD A 8 c D H<,) J x M(b) R lRAD) T x 1 z

?ART UNJF-U DlA :.01 * S3F D(A mm DIA D14

W,MnU

Ru U id) 1d) !,,

MAX MIN WIN ..010 .010 mx MI?.

-w -.OM

NASIM1 19M- 12 ; ~. 376 361 .12s 43 31$ .166 Mb 070 .020 010 46 I 05 m% OMS Dno

NM1CQ4 xOa-2t 2495

2470 439 ‘m ‘“ 3’ 398 “2 M6 076 010 0’0 ‘“ 0’ ; w ‘m’ 00’0

/

NASlw ,,~.,, \ ~ .,., .,,, ,,, , ,, ,W ,,, 0,0 ~ .0,, .020 0,0 632 06 ~ W8 ,CQ,, ,W]o

NAslmb ,17S0-14 3141

.3?20 ‘w ‘M ‘“ “5 “3 438 0’0 ‘w 02’ 0’5 ,63 I ~ I ,W I.w .W2,

I

Ntil M7 4375.20 ‘ 4370

.434, 6’9 ‘“ =0 7’ “ 4“ 0’0 ‘% ““ 0“ “’ ~ 0’ ~ 0,0 \m60 .W*, I

N&l M[ $W.zo , :yo 73, 74, 2s1 87 710 a, \ 070 ,Ob 1.0>0 .O*G; W21 08 boll I ;Oobo ~ ,W20

r

uslw9

! 10’0 141 ~o]$ ~o:u i ’47 i ‘y !012 ‘“ w’”

S6,3. ~, \ ,::: .176 , 86s 31> 101 13s 65.

I

N&lolo 615C-11 ‘~ .939 928 M41109 19s 714 070 141 040 i oz M’1”’l 013 00bo .00?0

NX1OI 1 .1500-16 ‘:2 IOU I 1051 406 123 1.023 87s 070 ~ 141 (us .030 1189 Iv I 011 ,W90 W1O

I

UA21014 87$0-14 :fi 1.131 1239 469 144 1.210 nd 070 l,, 0,0 035 I 336 II 020 GQ90 .m m

NASIOI. I.oma-11

‘~ !.UO 1.417 s]! 166 1398 1* 070 1.1 06D MS 1.48I 13 0:1 , Lmw 00>0

@ *d/v 4// (

NUIOI1 !.1150-11 ::;; ~ i 617 1614 594 1181585 !.188’[ “’”; 141 ‘ o~o 0$5] 16S8 I I) 025 m. ~,,

!

Ntit OaD 1.22m-]2 ; :5:1.s13 ‘Isa I 6s6 2.10 1.772 1.27s 070 141 07> 060 ) S46 13 028 0120 W20

t

“#* @ NAS1016AiNA_EmR DmfiNA_ Ju2.Y1.!979

LIST OF CURRENT SHFFTS

m

CUSTODIAN NATIONAL AEROSPACE STANDARDS CO~ITTEE

PROCUREMENT TITLE C.. ss,., c., ,o..

SPECIFICATION

STANDARD PART

BOLT - MACHINE

NONE HEXAGON HEAD , NON MAGNETIC, & HEAT RESISTANT NAS 1003THRL1 1020

SHEET 1 OF 3

md bv

Figure 32.—National aerospace standard for proper

@ AwO- IIldu,,rni

All r&*n .-M

fastener geometry.

4“. 1979

23 +
CODE BASIC PART NL’M9E? DESIGNATES .OMINti Di.4/METEh.

DASH :; Vh:BER DESIGN,A.lES CF.lP AND !. F.:,:GTH (SEE SHEET 3,.

A.iJO “.A” To DASH NUMBER FOP. UNDRILLEI) 39’.Z”

ADD “H”’ ?0 DASH SGMBER ‘OR DRi LLEfi ?.LF.~ ?!i! Y,

NO COL3E LE~ER DESlG~A7ES DRILLED S?hWK CNLY.

EWMPLE NAS1OO3-8 = .1900 DIA.VETEE BOLT. .509 GRIP, DRILLED SHANK ONLY.

NAS1OO3-8A = .1900 DIAMETER bOI.T. .5G2 CRI?, mDklLLED.

NAslo[~3-8ii = .1900 I) IA.METER b(>~r. .SOt) GRIP, DRILLED HE>J ONLY.

WTERLAL: CKES, A- 286 SPEC AMS573S OR AMSS7??,d?’$h4/&4/@.~~#~’fEXCE~ ULTIMATE @

TENSILE STRF.NGTI! 140,~0 PSI MINIM!:M AT RWJV TEMPERATURE, FABRICATED TO AMS7478.

rlNIsH CLEAN AND PASSIVATE !N ACCORDANCE ‘:, !TH.@~W’tip~’ @~-p-~S P

~)

Nc)r E5 i REFERENCE t)! StLSSIO?; S .ARE FOR Di.SIGN PURPOSES ONLY AND NOT AN lNSPll~lON Requirement.

2. MAGNETIC PERMEABILITY SHALL FE LISS Tt:.k}! 2.0 I AIR = 1.(IF FCJR A FICLO STRENGTII H = 2W OERSTEDS

(MAGNETIC PER! INABILITY INDICATOR ?:.!, :,ii~ .!. !72140R EQUi’i ALi hr )

.3 BCLTS S}l ALL BE I REE F?.Oh BURRS .\!JD 51. !VLRS.

4. THESE BOLrS ARE ltiTEhT!:[I J’OR [:SF ~.!, yr $,;~~ ?\<,~!!!\Ls I!?T() 12C,J P.

1., S. GRIP !. I.NGTH [ Kotl lji~h~ SI[}LGF Hi:,z.L :9 !:~i) 0{ {ULL CYLINDRICAL POR’:TC)N Or SII.+NK.

n (b) 6 CO~[F. ;’!X ;+OLE C: STI. RL[\: v, IT<\N (II f.; Ar; D !\c)R\l A;. wrtliN 2*OF BOLT CE:ff LRLINF.

~ ,<-,.

Id; 6.

{c’) g,

(el lo.

l!.

‘H” LIIA ?4LYlhfi’hl NO? TO tXCEEi. “L?”, ?<I: ,11.;u!,: D!.’, >.T TCP OF IIEAD N~i LESS TH,\N “H”.

Coh’c-E\’TRICITl” ““A””.AY;> “4” DlAh!7. TZ:~ “;JiT!i!N “;:” VALUE.S Tll? “A” AND THREAO PITCH DIAMETER

%lrlfip: “}’” VA1.L!ES TIR.

S!iANK STRAIGH”fW.SS. ‘A’Il”tllN “Z” V#LCi.L :!~.. ?ilt IYL!: OF L’-hG’ii{

BE.ARI!4G SURFACE SQUtiENZSS. V.?? Iilh .LI:.. TIP. WITH SHWK.

DIM L~Sl[>NS :S lN(’ti LS.

Figure 32.—Continued,

24
NATIONAL AEROSPACE STANDARD

AEROSPACE INDuSTRIES ASSOCIATION OF AMERICA INC 1725 DE SALES STREET N w WASHINGTON. D C 20036

ASHNO.INDICAIES GRIPLENCI’N IN.0625INCREMENTSI~*DIATEOR LONCER L2NCTHS MY BE ORDEP.SDBY USE OF PROPER DMH NO

Q

I ] NAS 1003 THR” 1020

Figure 32 ,–Concluded.

25
Flat Round Oval Fillister

Pan Binding Truss Plain

(carriage)

Figure 33. —Bolthead and screwhead styles

Rivets and Lockbolts

Rivets

Rivets are relatively low-cost, permanently installed

fasteners that are lighter weight than bolts. As a result, they

are the most widely used fasteners in the aircraft manufacturing

industry. They are faster to install than bolts and nuts, since

they adapt well to automatic, high-speed installation tools.

However, rivets should not be used in thick materials or in

tensile applications, as their tensile strengths are quite low

relative to their shear strengths. The longer the total grip length

(the total thickness of sheets being joined), the more difficult

it becomes to lock the rivet.

Riveted joints are neither airtight nor watertight unless

special seals or coatings are used. Since rivets are permanently

installed, they have to be removed by drilling them out, a

laborious task.

General Rivet Types

The general types of rivets are solid, blind, tubular, and

metal piercing (including split rivets). From a structural design

aspect the most important rivets are the solid and blind rivets.

Solid tivets. —Most solid rivets are made of aluminum so

that the shop head can be cold formed by bucking it with a

pneumatic hammer. Thus, solid rivets must have cold-forming

capability without cracking. A representative listing of solid

rivets is given in table IX (ref. 2 1). Some other solid rivet

materials are brass, SAE1006 to SAE1035, 1108 and 1109

steels, A286 stainless steel, and titanium.

Note that the rivets in table IX are covered by military

standard specifications, which are readily available. Although

most of the solid rivets listed in table IX have universal heads,

there are other common head types, as shown in figure 34.

However, because the “experts” do not necessarily agree on

the names, other names have been added to the figure. Note

also that the countersunk head angle can vary from 60” to 120”

although 820 and 100° are the common angles.

Washer Hex

Hex washer 10tt” heads.

TABLE 1X.–ALUMINUM AND OTHER RIVET MATERIALS

[From ref. 21.]

Material

2 117-T4

2024-T4

IIoi)

5056-H32

Mmrel

(annealed)

Copper

(annealed)

7050-T73

Rivet

designation

AD

DD

A

B

M

_——

E

Rivet heads

available

Universal (MS20470)

100” Flush (MS20426)

Universal (MS20470)

100” Flush (MS20426)

Universal (MS20470)

100” Flush (MS20426)

Universal (MS20470)

100” Flush (MS20426)

Universal (MS206 15)

100” Flush (MS20427)

100” Flush (MS20427)

Universal (MS20470)

100° Flush (MS20426)

Applications

General use for

most applications

Use only as an

alternative to

7050-T73 where

higher strength

is required

Nonstructural

Joints containing

magnesium

Joining stainless

steels, titanium,

and Inconel

Nonstructural

Use only where

higher strength

is required

The sharp edge of the countersunk head is also removed in

some cases, as in the Briles 13BRFZ “fast” rivet (fig. 35), to

increase the shear and fatigue strength while still maintaining

a flush fit.

Blind rivets. —Blind rivets get their name from the fact that

they can be completely installed from one side. They have the

following significant advantages over solid rivets:

(1) Only one operator is required for installation.

(2) The installation tool is portable (comparable to an

electric drill in size).

l~Briies Rivet Corporation, Oceanside, California

26
Button Truss Flat Countersunk Pan

(brazier) (flush) (universal)

Figure 34.—United States standard rivet heads.

~Shear-bearing area

\

Shear-bearing ‘Jarea

FigUre35. —BRFZ ‘faSt’ riVet.

(3) Theycan beusedwhere onlyone sideofthe workplace

is accessible,

(4) Agiven-length rivet can beusedfor arange of material

thicknesses.

(5) Installation time is faster than with solid rivets.

(6) Clamping force ismoreuniform thanwith solid rivets.

(7) Less training isrequired for the operator.

Blind rivets are classified according to the methods used to

install them:

(1) Pull mandrel

(2) Threaded stem

(3) Drive pin

Specific types (brands) of blind rivets are covered in

subsequent sections of this manual.

Pull-mandrel rivets: This rivet is installed with a tool that

applies force to the rivet head while pulling a prenotched

serrated mandrel through to expand the far side of the tubular

rivet. When the proper load is reached, the mandrel breaks

at the notch. A generic pull-mandrel rivet is shown in

figure 36.

~readed-stem rivets: The threaded-stem rivet (fig. 37(a))

has a threaded internal mandrel (stem) with the external portion

machined flat on two sides for the tool to grip and rotate. The

head is normally hexagonal to prevent rotation of the tubular

body while the mandrel in being torqued and broken off.

Drive-pin rivets: This rivet has a drive pin that spreads the

far side of the rivet to form a head, as shown in figure 38.

Although drive-pin rivets can be installed quickly, they are

Rivet inserted

Uu

Start setting

~

Figure 36.–Pu1l-mandrel rivet. (From ref. 5.)

usually not used in aerospace applications. They are used

primarily for commercial sheet metal applications.

Tubular rivets. -Tubular rivets are partially hollow and

come in a variety of configurations. The generic form has a

manufactured head on one side and a hollow end that sticks

through the pieces being joined. The hollow end is cold formed

to a field head.

Since extensive cold forming is required on these rivets, they

must be extremely ductile and are consequently made of lowstrength materials. They are normally used for commercial

applications rather than in the aerospace industry.

Some specific types of tubular rivets are

(1) Compression

(2) Semitubular

(3) Full tubular

27
gonal

(a)

*

Figure 38 .–Drive-pin rivet. (From ref. 5,)

Compression tubular rivets: A compression tubular rivet

(fig. 39) consists of two parts that have an interference fit when

driven together, These rivets are used commercially in soft

materials and where a good appearance is required on both

sides of the part.

Semitubular rivets: The semitubular rivet (fig. 40) has a hole

in the field end (hole depth to 1.12 of shank diameter) such

that the rivet approaches a solid rivet when the field head is

formed.

Full tubular rivets: The full tubular rivet (fig, 41) has a

deeper hole than the semitubular rivet. It is a weaker rivet than

the semitubular rivet, but it can pierce softer materials such

as plastic or fabric.

Metal-piercing n“vets.—Metal piercing rivets (fig. 42) are

similar to semitubular rivets, except that they have greater

column strength. Part of the sandwich material is not drilled,

and the rivet pierces all the way or most of the way through

while mushrooming out to a locked position.

Inserted Installed

installed

(b)

(a) One-piece body. (From ref. 5.)

(b) Two-piece body, (From ref. 22.)

Figure 37,—Threaded-stem rivets.

Figure 39.–Compression tubular rivet, (From ref. 5.)

Figure 40.–Semitubular rivet. (From ref. 5.)

Figure 41 .–Full tubular rivet. (From ref. 5.)

28
Figure 42.–Metal-piercing rivet. (From ref. 5.)

Figure 43.–Split (bifurcated) rivet. (From ref. 5.)

Split rivets. –Split (bifurcated) rivets (fig. 43) are the

standard “home repair” rivets. They have sawed or split

bodies with sharp ends to make their own holes through

leather, fiber, plastic, or soft metals. They are not used in

critical applications.

Specific Rivet Types

AD & DD solid rivets. -The most common solid rivets are

the AD and DD aluminum rivets, as listed in table IX. These

are the preferred rivets for joining aluminums and combinations of aluminum and steel. The “icebox” (DD) rivets can

be used in higher-strength applications, but they must be kept

around O 0F until they are installed. The 7050-T73 aluminum

rivets are an alternative to “icebox” rivets.

Since solid rivets are expanded to an interference fit, they

should not be used in composites or fiber materials. They can

cause delamination of the hole surfaces, leading to material

failure.

Cherry Buck n“vets.—The Cherry Buck rivet 14is a hybrid

consisting of a factory head and shank of 95-ksi-shear-strength

titanium, with a shop end shank of ductile titanium/niobium,

joined together by inertia welding (fig. 44). This combination

allows a shop head to be formed by bucking, but the overall

shear strength of the rivet approaches 95 ksi. The Cherry Buck

rivet can be used to 600 “F.

Monel rivets. —Monel (67 percent nickel and 30 percent

t4’f’o~nsend Company. Cherry River Division, Santa Ana, California.

(a) (

\ 4

(a) Minimum grip,

(b) Maximum grip.

Figure 44,—Cherry Buck rivet.

copper) rivets are used for joining stainless steels, titanium,

and Inconel. Monel is ductile enough to form a head without

cracking but has higher strength (F$U= 49 ksi) and

.:mperature capabilities than aluminum,

Titanium/niobium rivets. —These titanium alloy rivets (per

MIL-R-5674 and AMS4982) have a shear strength of 50 ksi

but are still formable at room temperature. They generally do

not need a coating for corrosion protection. The Cherry E-Z

Buck is a titanium/niobium rivet.

Cherry rivets.-The generic Cherry rivet is a blind structural

rivet with a locking collar for the stem installed as shown in

figure 45. (Different head types are available.) Cherry rivets

are available in both nominal and oversize diameters in the

common ( ~8 through ~ in.) sizes. The oversize rivets are used

for repairs where a nominal-size rivet (solid or blind) has been

drilled out or where the initial drilled hole is oversize. These

rivets have shear strengths comparable to AD solid aluminum

rivets. However, their usage is restricted in aircraft manufacturing by the guidelines of MS33522, which is included as

appendix C. A typical list of available Cherry rivet materials

is shown in table X.

Huck blind rivets. —Huck blind rivets 15 are similar to

Cherry rivets, except that they are available in higher strength

material, These rivets are made with and without locking

collars and with countersunk or protruding heads. Note also

(in fig. 46) that the sleeve on the blind side is deformed

differently on the Huck rivet than on the Cherry rivet.

tSHuck Manufacturing Company, Long Beach, California.

29
I

I

(a) Insert CheITyMAXrivet into prepared hole. Place pulling head over rivet stem and apply firm, steady pressure to seat head. Actuate tool.

(b) Stem pulls into rivet sleeve and forms large bulbed blind head; seats rivet head and clamps sheets tightly together. Shank expansion

begins.

(c) “Safe-lock” locking collar moves into rivet sleeve recess. Formation of blind head is completed. Shear-ring has sheared from

cone, thereby accommodating a minimum of [b in, in structure thickness variation.

(d) Dri\,ing anvil forms “safe-lock” collar into head recess, locking stem and sleeve securely together, Continued pulling fractures

stem, providing flush, burr-free, inspectable installation,

Figure 45.—Cherry rivet installation

TABLE X.–CHERRY RIVET MATERIALS Lockbolts

5055 Aluminum Alloy steel 50000

5056Aluminum CRES 50000

Monel CRES 55000

Into 600 Into X750 75000

Maximum

temperature

“F

250

250

900

1400

Pop n“vets.—Pop rivets ‘Gare familiar to most of the public

for home repairs. However, they are not recommended for

critical structural applications. The stem sometimes falls out

of the sleeve after the rivet is installed, and the symmetry of

the blind (formed) head leaves much to be desired. Although

the pop rivet shown in figure 47 is the most common type,

usMmakes a closed-end rivet and three different head styles.

ldus~ Corporation, Pop Rivet Division, Shelton, Connecticut

In general, a lockboh is a nonexpanding, high-strength

fastener that has either a swaged collar or a type of threaded

collar to lock it in place. It is installed in a standard drilled

hole with a snug fit but normally not an interference fit. A

lockbolt is similar to an ordinary rivet in that the locking collar

or nut is weak in tension loading and is difficult to remove

once installed.

Some of the Iockbolts are similar to blind rivets and can

be completely installed from one side. Others are fed into the

workpiece with the manufactured head on the far side. The

installation is then completed from the near side with a gun

similar to blind rivet guns. Lockbolts are available with either

countersunk or protruding heads.

Since it is difficult to determine whether a lockbolt is

installed properly, they should be used only where it is not

possible to install a bolt and nut of comparable strength,

However, they are much faster to install than standard bolts

and nuts.

30
PGrip7

s

e

P

type optional)

(a)

(a) Protruding head, BP-T (MS90354) or BP-EU

(b) Installed fastener,

Figure 46. —Huckb1ind rivets.

(b)

(MS21141).

Hi-Lok

The Hi-Lok]7 lockbolt has a countersunk or protruding

manufactured head and threads like a bolt. It is fed through

the hole from the far side. The installation gun prevents shank

rotation with a hexagonal key while the nut is installed (as

shown in fig. 49). The nut (collar) hexagonal end is notched

to break off at the desired torque. Hi-Lok lockbolts are

available in high-strength carbon steel (to 156-ksi shear),

stainless steel (to 132-ksi shear), and titanium (to 95-ksi shear).

3

Figure 47.—Pop rivet installation.

Jo-Bolts

Jo-bolts are similar to blind rivets in appearance and

installation. The locking collar (sleeve) is expanded to form

a shop head by rotating the threaded stem with a gun. The

threaded stem is notched and breaks off when the proper torque

is reached, A typical Jo-bolt installation is shown in figure 48.

Huckbolts

Huckbolts 15are similar to Hi-Loks except that the stem is

usually serrated rather than threaded. The collar is swaged

on the stem. Then the stem is broken at the notch as shown

in figure 50. Huckbolts and their collars are available in carbon

steel, aluminum, and stainless steel with various strengths, as

listed in the Huck catalog.

Taper-Lok

Taper-Lok 18 is a high-strength threaded fastener that is

17Hi.Shear Corporation, Torrance, California.

Issps Technologies, Jenkintown, peflflSylvaflia.

Typical installation

Figure 48.–Jo-bolt. (From ref. 21.)

31
~+1-+-: f

Remaining portion of

Hi-Lok collar after assembly

Collar wrenching

device automatically

shears off

(a) (b)

(a) Hi-Lc}k pin.

(b) Hi-Lok pin find collar after assenlbly

Figure 49. —Hi-Lok installation.

.

Figure 50.—Installed Huckbolt fastener.

L z Nominal grip

Thread length in 16ths

Forged head

Typical installation

Figure 5 1,—Tziper-Lok installation

installed with an interference fit. Most of the shank is tapered Rivnuts

on a 1.19° angle. The lubricated lockbolt is driven into a

drilled and reamed hole. The interference fit allows the nut

(tension or shear nut) to be installed and torqued to the required

value without holding the Iockbolt to prevent rotation (see

fig. 5 1). The nuts are locknuts with captive washers, When

a tension nut is installed, this fastener can take as much tension

load as a bolt of [he same size and material, Consequently,

Taper-Loks are used in critical applications where cyclic

loading is a problem. Taper-Lok Iockbolts are available in

A Rivnut ‘g is a tubular rivet with internal threads th:i[

deformed in place to become a blind nutplatc (fig. 52). Ri\ nuts

are available with protruding, countersunk, and filiister hc:ids.

They are also available with closed ends, sealed heads. ribbed

shanks, hexagonal shanks, and ribbed heads. Since the

unthreaded tubular portion of the rivet must deform. tht

material must be ductile. Consequently, the Ri\ nut m:tterials

are fairly low strength, as shown in table XI.

high-strength alloy steel, H-11 tool steel, and several stainless

steels, as well as titanium, IYB,F,G{)O~riCh, Engineered Sy\tenl\ Divisl{ln. .~hl’t~ll. [)hl(~.

32
1

(a) (b) (c) (d)

(a) Step 1–Rivnut fastener is threaded onto mandrel of installation tool.

(b) Steu 2—Rivnut fastener. on tool mandrel. is inserted into hole drilled for installation

(e)

(c) Step 3–Mandrel retracts’ and pulls threaded ~rtion of Rivnut fastener shank toward blind side of work, forming bulge in unthreaded

shank area.

(d) Step 4–Rivnut fastener is clinched securely in place; mandrel is unthreaded, leaving internal Rivnut threads intact.

(e) Blind nutplate–Properly installed Rivnut fastener makes excellent blind nutplate for simple screw attachments; countersunk Rivnut

fasteners can be used for smooth surface installation.

Figure 52. —Rivnut installation,

TABLE X1,–STANDARD RIVNUT FASTENER

MATERIALS AND FINISHES

Material Type Standard finish Minimum

ultimate

tensile

strength,

psi

iluminum 6053-T4 Anodize–Alumilite 205 28 ~

wiIl meet specifications:

MIL-A-8625 (ASG)

;teel C-1 108a Cadmium plate–O.0002 in. 45000

C-lllw minimum thickness per

QQ-P-416b, class 3,

type I

4037 Cadmium plate–O.0002 in. b55 000

minimum thickness per C85 ~

QQ-P-416b, class 2,

type II

;tainless 430 Picfded and passivated per 67 04)0

steel QQ-P-35, type n

305d None–bright as machined 80000

Carpenter lW

lrass A11oY260 None–bright as machined 50000

W- 110S and C-II 10 steel may be used interchangeably.

bNo 4 and No. 6 thread sizes.

CNO. S—1/2-in. thread size.

d305 and Car~nter No. 10 stalntess steel may be ud interchangeably

Hi-Shear Rivet

Hi-Shear’7 rivets consist of a high-strength carbon steel,

stainless steel, aluminum, or titanium rivet (pin) with a nakeddown shop head, as shown in figure 53. The collar (2024

aluminum or Monel) is swaged on to give a finished head that

t

Pin groove edge

L

—, must show

1, 1

Pin trimming edge

&

Collar

Figure 53 .—Hi-Shear installation.

can be visually inspected for proper form. This rivet should

be used for shear applications only, as the collar has negligible

tensile strength.

Although this rivet has been partially superseded by various

lockbolts, it is still being used in aircrafi and aerospace

applications.

Lightweight Grooved Proportioned Lockbolt

The lightweight grooved proportioned lockbolt (LGPL)20is

made especially for composite materials. It has both an

oversize head and an oversize collar to lessen contact stresses

zOMOnOgrarn,4erospaceFasteners,f..,osAngeles, California.

33
(a) (b)

t

(c)

+

(d)

(a) Flanged collar is placed over lightweight pin.

(b) Installation tool grips and pulls pin, drawing sheets tightly together and removing sheet gap.

(c) As pull on pin increases, tool anvil swages flanged collar into locking grooves and forms permanent vibration-resistant lock.

(d) Pull on pin continues until pin fractures at breakneck groove and is then ejected. Tool anvil disengages swaged collar.

Figure 54. —LGPL installation.

on tie composite material during both installation and service

life. The shank is high-strength (95-ksi shear) titanium and

the collar is 2024 aluminum. It is installed with a lockbolt tool

as shown in figure 54.

General Guidelines for Selecting Rivets

and Lockbolts

A number of standard documents are available for the

selection, installation, and drawing callout of rivets and

lockbolts as follows:

(1) Rivet installations are covered by MIL-STD-403. This

specification covers pilot holes, deburring, countersinking,

dimpling, and the application of zinc chromate paint between

dissimilar materials. Other specifications for corrosion

prevention of drilled or countersunk surfaces are covered in

MIL-P-116 and MIL-STD-171.

(2) Design and selection requirements for blind structural

rivets are given in MS33522 (appendix C).

(3) Design and selection requirements for blind

nonstructural rivets are given in MS33557.

(4) A wealth of information on allowable rivet strengths in

various materials and thicknesses is given in chapter 8 of

MIL-HDBK-5 (ref. 18).

(5) Testing of fasteners is covered by MIL-STD- 1312.

(6) Lockwiring is done per MS33540.

Note that the nominal rivet spacing for a rivet pattern is an

edge distance of 2D and a linear spacing of 4D, where D is

the rivet diameter. However, the 4D spacing can be increased

if sealing betwmn rivets or interrivet buckling is not a problem.

Solid rivets (expanded during installation) should not be used

in composite materials, as they can overstress the hole and

cause delamination of the material.

Lewis Research Center

National Aeronautics and Space Administration

Cleveland, Ohio, June 30, 1989

34
References

1. Slincy, HE.: High Temperature Solid Lubricants— 1. Layer Lattice

Compounds and Graphite. Mech. Eng., vol. 96, no. 2, Feb. 1974,

pp. 18-22.

2. Pret,ention uf Material Deterioration: Corrosion Control Course–U. S.

Army Logistics Engineering Directorate–Nov. 1970.

3, ASM Metals Handbook. 9th ed., Vols. 1, 2, 3, 5, 13, American Society

for Metals, Metals Park, OH.

4. SAE Handbook. SAE, 1968.

5. 1987 Fastening, Joining & Assembly Reference Issoe. Mach. Des.,

vol. 59, no. 27, Nov. 19, 1987.

6. Unified Inch Screw Threads (UN and UNR Thread Form). ANSI

B 1,1-1982, American National Standards Institute, New York, NY,

1982.

7. Screw Thread Standards for Federal Services, Part l–Unified UNJ

Unified Miniature Screw Threads. Natiowal Bureau of Standards

Handbook, NBS-H28-1969-PT-I, 1969.

8. Fastener Standards. 5th ed., Industrial Fasteners Institute, Cleveland,

OH, 1970.

9. Bickford, J. H.: An Introduction to the Design and Behavior of Bolted

Joints. Dekker, 1981.

10. Juvinall, R.: Engineering Considerations of Stress. Strain, and Strength.

McGraw-Hill, 1967.

11. Donald, E. P.: A Practical Guide to Bolt Analysis. Mach. Des., vol. 53,

Apr. 9, 1981, pp. 225-231.

12. Baumeister, et al.: Mark’s Standard Handbook for Mechanical Engineers.

8th ed., McGraw-Hill, 1978.

13. Seely, F. B,: Resistance of Materials. 3rd ed., Wiley & Sons, 1947.

14. Shigley, J. E.; and Mitchell, L. D.: Mechanical Engineering Design. 4th

cd., McGraw-Hill, 1983.

15. Machine Design, Nov. 19, 1981.

16. Peery, D.J.: Aircraft Structures. McGraw-Hill, 1950.

17. Grinter, L.: Theory of Modern Steel Structures. Vol. I, Macmillan

co., 1955.

18. Metallic Materials and Elements for Aerospace Vehicle Structures.

MIL-HDBK-5E, Department of Defense, June 1987.

19. Faupel, J. H.; and Fisher, F. E.: Engineering Design, 2nd ed., Wiley &

Sons, 1981.

20. Fastener Technology International Magazine, Solon, Ohio, Ott. 1985

through Feb. 1987 Editions.

21. Design Handbook, Section 16. McDonnell Douglas Astronautics Co.,

Huntington Beach, CA.

22. Bruhn, E. F.: Analysis & Design of Flight Vehicle Structures. Tri-State

Offset Co., Cincinnati, 1965.

35
Appendix A

Bolthead Marking and Design Data

[From ref. 20]

36

38
znn

39

III
.

.

..-.

.<

II

42
43
44

46
I

I

I

J

3

J,

n

3

I

47
. -.

ix

II

50

I

52

54

Zu=

~mm

-00

n

--

—

56
in.-Q

57
58
-

-

-

E

-

59
I

,

II

I

I

I

I

1’

+

I

I
61
I I

I I

I

I I I

,.:

.\= ..< >.:
,

63
>

E

m

mL

..

.,

au

cOu

z?!

I

.7

.

i

I

64

}

t

66

68

. .

--

c

-.

G

70
71
1

I

I

I

>:

x

L

L

--

.

/,;

.,-.—

I

k-

—

.

x

>,-

72
73
xc1u

74
Ill

0

0.

z. —

I

,!

—

75

—...

I

I

I

77
i!

I

I

i,’

78
79
80
I

U) u
>

>

;

1.

)

i

i

&

)

)

—

82
07

@i 4Z

83
>

>

i

L

>

i

i

>

i

>

>

—

84
II

!
-

w

m
87
88
6uI!IJeuJOAlleUlell~

89
Appendix B

Bolt Ultimate Shear and Tensile Strengths

[From ref. 18]
AIIL-HDBK-5E

1 June 1987

,

I

I

I —-
MILHDBK-5E

1 June 1987

—

—

—

mm

-m 3 ---

000

92
MIL-HDBK-5E

1 June 1987

-c

c

93
Appendix C

Blind Rivet Requirements

94
E

BLIND RIVETS SMLL BE usEO IN Compliance U[TH THE JOINT ALLOUABLE TMLfs IN mlL-Hw K-5, CHAPTER 8.

BLIND RIVETS SfflLL CWFOPM TO THE FOLLOUING REQuIREMENTS :

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

THE HOLE SIZE FOR BLIND INSTALLATION StlALL BE wITHIN THE LIMITS SPECIFIEO W THE APPLICABLE

s? EDIFICATION SHEET, STANOARD, OR OPAUING,

FOR OIMPLEO AssEtmLY, THE RIVET HOLEs WALL BE S12E0 AFTER THE SNEETS HAVE BEEN OIWLEO.

MECHANICALLY LOCKEO SPINOLE BLINO RIVETS (LOCKING RI!G OR COLIAR) MY BE USEO CN AIRCRAFT

IN AIR INTAKE AREAS ANO IN THE AREA FORHAROOF THE EtiGINE.

FOR REPAIR ANO P.EUORK, THE BLINO RIVETS LISEO IN REPL?,CEHENT OF W1O SHANK RIVETS SMLL Bf

OVERSIZE OR WE STANOARO SIZE LARGER (sEE REOW 5).

0VERS12E BLIND RIVETS WY BE USEO FOR REPA[R ANO REWORK:

a. OVERSIZE R[VETS ARE FOR uSE IN Nml-STANDARO WLE OIANETERS. N~4-STANMRO HOLES

ARE THE RESULT OF HOLE RES] ZING OURING REHORK OR REPAIR, OR OUE TO MNUFACTWING

ERROR IN NEu OESIGN.

b. THE GQIP LENGTH OF THE OVERSIZE RIVET, THE BACKS1OE CLEARANCE (INsTALLEO AND

UNINSTALLED) , ANO THE PERFORMANCECNAR4CTERISTICS SHALL BE EQML TO THE STAHMRO

RIVET THAT IS BEING REPLAC1O.

E’ I:,LI RIVETS SHALL NOT BE LISEC:

a. IN FLUID TIW AREAS

b. W AIRCRAFT C~TROL SmFACE HINGES, HINGE BRACKETS, FLIGHT CONTROLACTUATING

sysTE~s. uING AmAC~lENT F [TT INGS . LANOING GEAR FITTINGS. OR OTNER N~VILY

STRESSEO LOCATlfflS ON THE AIRCRAFT,

FRICTl~ LOCKED BLINO RIVETS (NO LWKING RING OR COLLAR) WALL NOT BE USEO

W AIRCRAFT IN AIR INTAKE AREAS WHERE RIVET PARTS WY BE INGESTED BY THE ENGINE.

NICKEL-COPPER ALLOY (HONEL) RIVETS uIT!i CAMIW PLATING SNALL NOT BE USEO

WHERE THE A~IENT TEMPERATURE IS ABOVE 400” F.

FLUSH HEAO RIVETS SHALL NOT BE MILLED TO OBTAIN FLUSHMESS UITH THE

SURROUNOING SHEET WITHOUT PRIOR URITTEN APPROVAL FROM TH[ OESIGN ACTIVITY.

OVERSIZE BLINO RIVETS SHALL NOT BE SPECIFIEO IN NEI{ OESIWi. AN OVERSIZE

BLINO RIVET [S ONE SPECIFICALLY OESIGNEO FOR REPLACE!S~lT PURPOSES. ITS

WANK OIAt4ETER OIMENSION IS GREATER THAN A STANOAROBLI>ICI RIvET.

CJiEHICALLY EXPANOEO BLIND RIVETS SNALL NOT BE USED.

THIS IS A OESIGN STANOARO, NOT TO BE IJSEO AS A PART NWBER.

@ REwR,TTZN

.A. nm

(AW - U MiLITARY STANDARD nk cuti RIVETS . BLIND, STRUCTURAL. f!ECtiN{l CALLY LOCKEO ANO

FRICTl OII R[rAl:/fR SPI!ICLE. (Rf LIfi51Ll TY h~o NAIHTAINABILITY)

Am - AV OES I GN ~10 CO:iSTRUCTIOll REQUI REf:ENTS FOR.

USAF - 11

1 ! MS33522

MWURUXN7 s? fcillu3ToM Sunuxou: Wm 1 of ,

, I

DD ,%. 672-1 ~ ——wm. .— PROJECT NO. 5320-0375 ‘“m=

95
Nattonal Aeronautics and Report Documentation Page

Space Adm(nlstratlon

1. Report No. 2. Government Accession No. 3. Recipient’s Catalog No.

NASA RP-1228

4. Title and Subtitle 5. Report Date

Fastener Design Manual March 1990

6. Performing Organization Code

7, Author(s) 8. Performing Organization Report No.

Richard T. Barrett E-49 11

10. Work Unit No.

9, Performing Organization Name and Address

11. Contract or Grant No.

National Aeronautics and Space Administration

Lewis Research Center

Cleveland, Ohio 44135-3191 13. Type of Report and Period Covered

2. Sponsoring Agency Name and Address Reference Publication

National Aeronautics and Space Administration 14, Sponsoring Agency Code

Washington, D. C. 20546-0001

5. Supplementary Notes

6. Abstract

This manual was written for design engineers to enable them to choose appropriate fasteners for their designs.

Subject matter includes fastener material selection, platings, lubricants, corrosion, locking methods, washers,

inserts, thread types and classes, fatigue loading, and fastener torque. A section on design criteria covers the

derivation of torque formulas, loads on a fastener group, combining simultaneous shear and tension loads, pullout

load for tapped holes, grip length, head styles, and fastener strengths. The second half of this manual presents

general guidelines and selection criteria for rivets and lockbolts.

17. Key Words (Suggested by Author(s)) 18. Distribution Statement

Fastener design; Washers; Inserts; Torque table; Unclassified-Unlimited

Rivets; Lockbolts Subject Category 37

19. Security Classif, (of this report) 20. Security Classif. (of this page) 21. No of pages 22. Price’

Unclassified Unclassified 100 A05

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NA3A runm 10LO UL 1 Ub *For sale by the National Technical Information Service, Spnngfleld, Virginia 22161

NASA-L8ngley, 1~