**Process Specification for Installation of Threaded and Collared
Fasteners**

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| **Engineering Directorate**                                           |
|                                                                       |
| **Structural Engineering Division**                                   |
|                                                                       |
| February 2007                                                         |
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| ![](media/image1.png){width="1.3944444444444444in"                    |
| height="1.1430555555555555in"}                                        |
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| National Aeronautics and                                              |
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| Space Administration                                                  |
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| **Lyndon B. Johnson Space Center**                                    |
|                                                                       |
| Houston, Texas                                                        |
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**Process Specification for Installation of Threaded and Collared
Fasteners**

+--------------+------------------------------------+-----+-----------+
| **Prepared   |                                    |     |           |
| by:**        |                                    |     |           |
+--------------+------------------------------------+-----+-----------+
|              | Jay E. Bennett                     |     | Date      |
|              |                                    |     |           |
|              | Materials and Processes Branch     |     |           |
|              |                                    |     |           |
|              | ES4                                |     |           |
+--------------+------------------------------------+-----+-----------+
|              |                                    |     |           |
+--------------+------------------------------------+-----+-----------+
|              |                                    |     |           |
+--------------+------------------------------------+-----+-----------+
| **Approved   | Bradley S. Files, Chief            |     | Date      |
| by:**        |                                    |     |           |
|              | Materials and Processes Branch     |     |           |
|              |                                    |     |           |
|              | ES4                                |     |           |
+--------------+------------------------------------+-----+-----------+
|              |                                    |     |           |
+--------------+------------------------------------+-----+-----------+

  ----------- --------------------------------------------- ---------------
  REVISIONS                                                 

  VERSION     CHANGES                                       DATE

  \--         Original version                              7/13/00

  A           Changed Division name. Revised Section 3.1    10/2004
              (Work Instructions) and moved to Section 6.1, 
              renumbered Section 6, and revised Section 9.0 
              (Training).                                   

  B           Updated document number for JPR 8500.4 in     2/2007
              Section 4.0 (References)                      

                                                            

                                                            
  ----------- --------------------------------------------- ---------------

**1.0 [SCOPE]{.underline}**

This process specification establishes the engineering requirements for
the installation of threaded and collared fasteners, including
conventional threaded fasteners, and Hi-Lok fasteners.

**2.0 [APPLICABILITY]{.underline}**

This specification shall be applicable whenever the installation of
threaded or collared fasteners is invoked per section 3.0, "Usage".

**3.0 [USAGE]{.underline}**

Manufactured heads are on the forward or near side relative to the
engineering drawing, unless otherwise noted. The quantity of washers and
their location (under head or nut) shall be specified.

Fastener size and hole size shall be specified on the engineering
drawing. When countersink washers are not used under fastener heads, an
appropriate radius or chamfer shall be specified on the fastener hole to
accommodate the fastener fillet radius.

The included angle of a countersunk fastener or dimple shall correspond
to that of the flush fastener being installed. The diameter and depth of
the countersink or dimple shall be specified on the engineering drawing
so that the fasteners will meet the standard flushness requirement of
0.010 inch above the surface and 0.002 below. Alternate flushness
tolerances shall be specified on the drawing.

This process specification shall be called out on the engineering
drawing with a drawing note. For example:

INSTALL FASTENERS PER NASA/JSC PRC-9007. TORQUE 190-210 IN-LBS ABOVE
LOCKING TORQUE. LOCKING TORQUE SHALL BE 6.5-60 IN-LBS.

For conventional threaded fasteners, the net torque and locking torque
shall be specified by the engineering drawing. These torques may be
included in the process specification callout (as above), or they may be
located in the field of the drawing near the appropriate joint for
clarity, or an assembly specification referenced by the engineering
drawing.

The locking torque will be measured by the installation technician and
added to the net torque on the engineering drawing to determine the
installation torque for each fastener.

The locking torque shall be called out on the engineering drawing.
Normally, the range specified is obtained from the procurement
specification for the locking element, such as MIL-DTL-25027,
MIL-DTL-18240, MIL-I-45914, MIL-I-45932, and NASM8846.

Wet installation of fasteners with corrosion preventative primer is
standard. An example callout is:

SEAL FASTENER PER NASA/JSC PRC-4004 USING XXXXX SEALANT.

This callout should immediately follow the installation specification.
In some design cases, sealant may not be necessary, but the decision to
not use sealant should be reviewed in advance with Materials and
Processes Branch (ES4) personnel.

Fastener joints should be designed so that proper grip or fastener
length will be achieved during installation. However, the grip/length of
bolts/screws and the number of washers used will be changed during
assembly if necessary to achieve proper grip/length and locking feature
engagement unless specifically prohibited by the drawing note, such as:

NO GRIP SUBSTITUTIONS OR WASHER CHANGES ALLOWED.

Details of allowable grip/length substitutions and washer number changes
for bolt/screw installation are found in section 6.2 and 6.3.

**4.0 [REFERENCES]{.underline}**

All documents listed are assumed to be the current revision unless a
specific revision is listed.

SOP-007.1 *Preparation and Revision of Process Specifications*

JPR 8500.4 *Engineering Drawing System Manual*

NASA/JSC PRC-4004 *Sealing of Joints and Faying Surfaces, PRC for the*

MIL-DTL-25027 *Nut, Self-Locking, 250F, 450F. and 800F*

MIL-DTL-18240 *Fastener Element, Self-Locking, Threaded Fastener, 250F
Maximum*

MIL-I-45914 *Insert, Screw Thread - Locked In, Key Locked*

MIL-I-45932 *Insert, Screw Thread, Thin Wall, Locked In*

NASM8846 *Inserts, Screw Thread, Helical Coil*

1.  **[MATERIAL REQUIREMENTS]{.underline}**

    None identified.

**6.0 [PROCESS REQUIREMENTS]{.underline}**

**6.1 WORK INSTRUCTIONS**

All work shall be performed to written procedures. The work instructions
shall contain sufficient detail to ensure that the manufacturing process
produces consistent, repeatable products that comply with this
specification.

For work performed at JSC facilities, these work procedures consist of
Detailed Process Instructions (DPI's).

For contracted work, the contractor shall be responsible for preparing
and maintaining, and certifying written work procedures that meet the
requirements of this specification.

**6.2 GENERAL REQUIREMENTS**

Holes shall be verified as deburred before fasteners are installed.

No lubricant or sealant shall be applied to fasteners or threads unless
it is specifically called out on the engineering drawing.

Locking torque shall be measured during installation and verified to be
within the minimum-maximum range. Fasteners with locking torques found
outside the range shall be replaced using the appropriate materials
review board activity.

Fasteners removed shall be reinstalled to the same procedures as for new
fasteners. Fasteners shall be examined for wear or deformation before
being reinstalled.

3.  **SPECIAL REQUIREMENTS FOR SHANKED THREADED FASTENERS**

The proper grip shall be verified during assembly of the joint. Proper
grip is that range where there are no threads within the members being
joined, nor does the nut bottom on the shank of the fastener.

Bolt/screw shall protrude one full thread length, including the chamfer,
beyond the end of the nut or insert. When the locking feature is located
on the bolt/screw, the locking feature, or at least a portion of the
locking feature equal to one thread diameter, shall be engaged in the
internal thread.

Unless disallowed by the engineering drawing, changes to the bolt/screw
grip or to the number of washers can be made during the assembly process
to achieve proper grip and ensure engagement of the locking feature.
Bolts/screws one grip increment longer or shorter may be substituted.
One or two additional washers may be added, or one less washer may be
used than specified, as long as there was at least one washer specified
at that location. No less than one washer may be left where only one was
specified. Grip substitutions and washer changes are not permitted for
bolts/screws used with threaded inserts or barrel nuts.

Substitute bolts/screws shall be identical to those called out on the
drawing except for the grip difference. Extra washers shall be identical
to the original washer specified.

4.  **SPECIAL REQUIREMENTS FOR FULL THREADED FASTENERS**

The proper length shall be verified during assembly of the joint. Proper
length is that range where the bolt/screw shall protrude a minimum of
one full thread length, including chamfer, beyond the end of the nut or
insert. When the locking feature is located on the bolt/screw, the
entire locking feature, or at least a portion of the locking feature
equal to one thread diameter, shall be engaged in the internal thread.

Unless disallowed by the engineering drawing, changes to the bolt/screw
length or to the number of washers can be made during the assembly
process to ensure engagement of the locking feature. Bolts/screws one
length increment number longer or shorter may be substituted. One or two
additional washers may be added, or one less washer may be used than
specified, as long as there was at least one washer specified at that
location. A washer cannot be omitted where only one was specified.
Bolt/screw length substitutions and washer changes are not permitted for
full threaded bolts/screws used with threaded inserts or barrel nuts.

Substitute bolts/screws shall be identical to those called out on the
drawing except for the length difference. Extra washers shall be
identical to the original washer specified.

**6.5 SPECIAL REQUIREMENTS FOR COLLARED FASTENERS**

Proper hand or pneumatic equipment shall be used to install Hi-Lok
fasteners.

Perpendicularity of hole axis to surface shall be [+]{.underline} ½
degree. Maximum tilt or gap under protruding or flush head pins shall be
0.002 inch, one side only. No gap is permitted between the faying
surface at the fastener shank. Collars shall not engage the first
imperfect thread adjacent to the pip grip. Nuts shall not be loose,
cracked or split nor exhibit abnormal shear fracture. Nuts shall not be
removed and reinstalled. Pins shall not have sheared threads. The
threaded pin end shall not be fractured. Manufactured heads shall not
have cracks or dimple.

The pin shall extend beyond the surface of the material attached as
shown in Table 1. Any length pin may be used to comply with this
requirement as long as it is otherwise identical with the pin specified
on the engineering drawing.

[Table 1 Hi-Lok Pin Extension]{.underline}

  ---------------- ----------------- ----------------- ------------------
  Fastener                           Extension         

  Dash No.         Size              Minimum           Maximum

  -05              (0.164)           0.302             0.384

  -06              (0.190)           0.315             0.397

  -08              (0.250)           0.385             0.467

  -10              (0.312)           0.490             0.572

  -12              (0.375)           0.535             0.617

  -14              (0.437)           0.625             0.707

  -16              (0.500)           0.675             0.757
  ---------------- ----------------- ----------------- ------------------

Locking torque is not verified during installation of Hi-Loks.

**6.6 TORQUE WRENCH SELECTION**

All torque wrenches shall be verified to be in calibration before they
are used.

Torque wrenches shall only be used between 20 and 80 percent of their
torquing capability (middle 60 percent of full scale). Extensions do not
apply.

**6.7 TORQUE APPLICATION**

Fasteners shall be tightened to the installation torque specified by the
engineering drawing. The installation torque shall be established for
each bolt/screw by measuring the actual locking torque, and adding it to
the net torque. Fasteners shall be tightened from the nut side whenever
possible. Fasteners tightened from the head side should be torqued to
the high side of the specified torque range.

**7.0 [PROCESS QUALIFICATION]{.underline}**

None required.

**8.0 [PROCESS VERIFICATION]{.underline}**

Joints requiring secondary verification of assembly torque and the
recording of torque values shall have this indicated on the engineering
drawing or in the assembly procedure referenced by the engineering
drawing.

Assembled joints shall be visually inspected to verify the requirements
of Section 6.0 that can be determined visually.

Torque audits made at a later time to verify torque shall only be
conducted under appropriate materials review board (MRB) activity. When
they are conducted, torque audits shall be measured in the tightening
direction.

**9.0 [TRAINING AND CERTIFICATION OF PERSONNEL]{.underline}**

This process shall be performed by personnel qualified through training
or experience and certified by their supervision to conduct the process.

**10.0 [DEFINITIONS]{.underline}**

Locking Torque Torque required to turn the bolt/screw through the
locking feature of the nut while in motion in either the installation or
removal direction, without preload on the fastener. Also known as
"running torque".

### Net Torque Installation torque minus the locking torque