n ji Ji ^ M T - /rstudy of Handcuff Improvements

Product Performance Engineering Division

Center for Consumer Product Technology

National Engineering Laboratory

Prepared by

Law Enforcement Standards Laboratory

Center for Consumer Product Technology^

National Bureau of Standards

Washington, D.C. 20234

Issued April 1980

Prepared for National Institute of Justice

U.S. Department of Justice

shington, D.C. 20531

James E. Harris

a

National Bureau of Standards

March 1980

MATIONAL BUREAU OF STANDARDS

LIBRARY NBSIR 80-1989

A STUDY OF HANDCUFF IMPROVEMENTS

James E. Harris

JUN 5 1980

Mor AC-C..' E.EF

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Product Performance Engineering Division

Center for Consumer Product Technology

National Engineering Laboratory

National Bureau of Standards

Prepared by

Law Enforcement Standards Laboratory

Center for Consumer Product Technology

National Bureau of Standards

Washington, D.C. 20234

March 1980

Issued April 1980

Prepared for National Institute of Justice

U.S. Department of Justice

Washington, D.C. 20531

U.S. DEPARTMENT OF COMMERCE. Philip M. Klutznick. Secretary

Luther H. Hodges, Jr., Deputy Secretary

Jordan J. Baruch, Assistant Secretary for Productivity, Technology, and Innovation

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

ACKNOWLEDGMENTS

This report v/as prepared by the Lav7 Enforcement Standards

Laboratory of the National Bureau of Standards under the direction

of Jacob J. Diamond and Lawrence K. Eliason, successive Chiefs of

LESL, and edited by Daniel F. Frank, Manager, Security Systems

Program. Its preparation was sponsored by the National Institute

of Justice, Lester D. Shubin, Standards Program Manacrer.

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Contents

Page

Summary

Introduction

Description of Operation, Standard Handcuffs

Description of Operation, Modified Handcuffs

Alternate Restraining Devices 1

Results 15

Other Potential Handcuff Improvements 16

Conclusion 19

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FOREWORD

The Law Enforcement Standards Laboratory (LESL) of the

National Bureau of Standards (NBS) furnishes technical support to

the National Institute of Justice (NIJ) program to strengthen law

enforcement and criminal justice in the United States. LFSL's

function is to conduct research that will assist law enforcement

and criminal justice agencies in the selection and procurement of

quality equipment.

LFSL is: (1) Subjecting existing equipment to laboratory

testing and evaluation and (2) conducting research leadina to the

development of several series of dociiments , including national

voluntary equipment standards, user guides and technical reports

This document covers research on law enforcement equipment

conducted by LESL under the sponsorship of NIJ. Additional

documents are being issued under the LESL program in the areas of

protective equipment, communications equipment, security systems,

weapons, emergency equipment, investigative aids, vehicles and

clothing

Technical comments and suggestions concerning this document

are invited from all interested parties. They may be addressed to

the author or to the Lav; Enforcement Standards Laboratory,

National Bureau of Standards, VJashington, DC 20234.

Lawrence K. Eliason, Chief

Law Enforcement Standards Laboratory
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A Study of Handcuff Improvements

James E. Harris

Product Performance Engineering Division

Center for Consumer Product Technology

National Bureau of Standards

Washington, DC 20234

SUMMARY

Designs for improving the security of present day ratchet and

pawl metallic handcuffs are presented, Tv;o methods utilizing a

new lock feature were developed that significantly improve the

lock. The National Bureau of Standards has applied for a patent

on these innovations. In addition, several other potential

handcuff improvements are discussed in this report.

INTRODUCTION

The use of a metallic handcuff as a temporary restraint of

individuals is an everyday occurrence, Hov^ever, since the present

handcuff was introduced two developments have occurred. First,

some individuals have obtained an alarming level of skill in

defeating the design, and second, the user population has

requested more security from the device than it presently

provides

1
In order to determine the present metallic handcuff problems

and to explore possible solutions to the identified problems,

meetings were held with manufacturers, distributors, instructors,

users, and other knowledgeable persons. Among the persons

consulted were the instructors and armory experts at the Federal

Bureau of Investigation Academy and members of the International

Association of Chiefs of Police. In addition, a large

manufacturer of law enforcem.ent equipment was visited to observe

their handcuff manufacturing process. Further information vras obtained by examining handcuffs that had failed in various ways.

Users of handcuffs have reported that most of the available

handcuffs are in need of improved lock security (pick resistance)

and increased strength for sv/ivels, chain links, rivets and

pivots. The primary objective of this project was to investigate

improvements to existing handcuff designs that could be

accomplished with mdnor modifications to existing tooling and

manufacturing processes. In addition, the procedures presently

used in the application of handcuffs should not be significantly

increased in complexity.

A handcuff is a temporary restraining device. Its purpose is

to contain a person for a short duration and under proper

surveillance. Hov/ever , arresting officers may sometimes be

preoccupied with other matters or otherv^ise unable to maintain

proper surveillance. Under these abnormal conditions, it is

2
desirable that metallic handcuffs continue to provide a reasonable

level of security.

DESCRIPTION OF OPERATION, STT^DARD HANDCUFFS

The operation of an ordinary handcuff can be understood by

referring to figure 1 in conjunction with the following

description. When open, the ratchet pivotes freely about the

ratchet pivot toward the main body of the handcuff until the teeth

of the ratchet engage the teeth of the pawl . Further ratchet

movement v/ill cause the spring-loaded pawl to cam up away from the

ratchet each time the teeth on the ratchet move over the teeth on

the pawl. When the ratchet motion stops, the pavrl is forced

against the ratchet locking the teeth together. This is the

primary locking means. The motion of the ratchet may be continued

to a desired amount of closure about an object (a wrist) . If

there is no object present to prevent continued motion, the

ratchet motion may be continued until the ratchet completely

passes the pawl. The shapes of the ratchet and pav;l teeth, v;hen

engaged, and the spring action are such that the ratchet motion is

possible in one direction only. In order to open the handcuff

when the teeth are engaged, the pawl must be disencraged (against

the pawl spring force) from the ratchet teeth. That is the

function of the key when unlocking the primary lock . Notice that

the pawl is able to move against the pawl spring force only when

3
Figure 1. Partial cross section of a typical handcuff with

the double lock bolt in the inactive position.
the double lock bolt is set to the inactive position (fig. 1 shows

the double lock inactive) . When the handcuff is closed to the

desired position, the rear tip of the key is then inserted into

the pusher hole to engage and press upon the pusher, innving the

double lock bolt to the active position as shov^n in fiaure 2.

With the bolt in this position, the pawl is not able to cam

sufficiently to enable the ratchet and pawl teeth to disenaage

because of the interference between the bolt and the pav/l

Accordingly, the ratchet cannot be closed further, nor can it be

opened. The hancuff is then said to be double locked. No method

has been discovered to enable a double locked handcuff to he

opened without first moving the bolt to the inactive position

unless some parts are physically distorted, or cut.

To open a double locked handcuff, the double lock bolt must he

moved away from the pawl as shown in figure 2 (key turns

clockwise) . Only after this is done can the tang of the key or a picking tool lift the pawl (against the pav;l spring force) away

from the ratchet (key turns counterclockwise). In this position,

the teeth of the pawl and ratchet are no longer engaged and the

ratchet is free to swing in either direction. It should be

observed that the function of the pawl spring is two-fold: to

retain the pawl against the ratchet to effect the primary locking,

and to provide a detent that maintains the double lock bolt in

either the active or inactive position. In most handcuffs a properly directed sharp impact of the handcuff against a hard

5
Figure 2 Partial cross section of a typical handcuff with

the double lock bolt in the active position.

6
object can defeat the detent function of the pav;l sprina and cause

the bolt to move. It is also a simple matter for a skilled person

to move the double lock bolt to the inactive position with a paper

clip or similar implement. If the double lock bolt moves to the

inactive position, it is then possible to open the lock v/ith a

picking tool such as a bent paper clip wire, or with a thin shim

that may be inserted between the pawl and ratchet to separate the

teeth. If the double lock bolt moves to the active position, the

handcuff must be "unlocked” prior to its use. In either case, the

ability to move the double lock bolt by a means other than the key

is undesirable.

DESCRIPTION OF OPERATION, MODIFIED HANDCUFFS

The modified (improved lock) handcuffs that were developed

during this study operate on the same principle as the standard

handcuff with the following additions. The improved handcuff has

means to automatically lock the bolt in the active position.

Locking of the bolt in the active position is called triple

locking. Refer to figure 3 to follow the operation of the triple

locking feature. When the double lock bolt is moved fully to the

active position, the pawl spring nov/ forces the corner of the bolt

against the housing wall, so that movement to the inactive

position is prevented by a ledge inside the handcuff housing.

Once the double lock bolt is active, it can only be moved to the

7
inactive position by unseating it from the lec'ge so that the

corner of the bolt will clear the corner of the ledge. It can be

seen that the bolt must be unseated prior to and during lateral

motion when the bolt moves to the inactive position. As before,

the lateral motion of the bolt is caused by the tang of the kev or

the picking tool.

DETENT

PAWL SPRING

PAWL

RATCHET

Figure 3. Cross section of a modified handcuff with the

double lock bolt active and held in place by

a locking ledge.

8
Two methods have been developed to unseat the bolt under

normal operation. One method of unseating the bolt is by the use

of a second key which is inserted through a nev; secondary keyhole

located on the opposite side of the handcuff from the standard or

primary keyhole as shown in figure 4. Rotation of the second key

causes the tang to move the bolt dovmward and av/ay ( unseat ina)

from the ledge. The standard or primary key is inserted throuah

its keyhole and this second key is rotated so that the tang of the

key moves the bolt to the inactive position. Both keys or two

picking tools must be operated simultaneously to unlock the

handcuff and since they are from the opposite sides of the

handcuff the skill required is high. This results in a difficult

feat for a handcuffed person to perform, which improves the

security features of the lock. A second method of unseating the

bolt is to use a hollow swivel with a concentric protruding pin

that serves as a push rod when the chain link within the eye of

the swivel is grasped and pressed upon the tip of the protrudina

pin as shown in figure 5. The pin transmits a force that presses

the bolt downward and away (unseating) from the ledge. The key

must then be inserted and rotated so that the tang of the key

moves the double lock bolt to the inactive position. The action

of grasping and pressing of the chain link against the pin to

unseat the bolt must be done simultaneously with the turning of

the key. These operations are difficult to perform by a

handcuffed person because they require a high degree of manual

dexterity. The security of the handcuff lock is thereby improved
Figure 4. Partial cross section of a modified handcuff

showing the secondary keyhold for unseating the

double lock bolt and the chamfer of the last

tooth of rachet.

10
I

(
Figure 6. Partial cross section of improved handcuff v/ith

the double lock bolt inactive.

12
Figure

7.

Photograph

of

the

demonstration

model

of

the

improved

handcuff.
design of the geometry of the lever and its pivot, it will he

impossible to apply excessive squeezing pressure to the wrist

because the lever will activate the double lock and prevent

further closure of the handcuff. Officers v/ill not need to use

the key to activate the double lock, a maneuver that is difficult

to do in the dark or with a hostile individual. Also, officers

will not forget to activate the double lock since this improvement

causes automatic multiple locking. If combined with the previous

improvement, triple locking is effected automatically when the

double lock is activated.

The improvement of automatically triple locking makes it very

unlikely that any directed shock would be able to unseat and

unlock the bolt. In order to accomplish this, one shock would be

required to unseat the bolt and while the bolt was unseated

against the pawl spring force, a second shock at a right angle to

the first would be required to move the bolt to the inactive

position. It is very unlikely that anyone would be skillful

enough to apply such shocks in the proper direction, intensity and

sequence even if they knew how these shocks were required.

Finally, it is doubtful if a single shock could replace the two

right-angled components because of the internal friction of the

sliding bolt against the ledge.

14
ALTERNATE RESTRAINING DEVICES

The improvements cited in this report are generally applicable

to other handcuff-like restraints. Some of these restraints are

j! leg irons, belly chains, leg chains, transportation belts, and

hobbles. Since there is sufficient variation in the design, each

I

,

i product would require a detailed examination to determine the

[

i aptness of any of these changes.

j

RESULTS

Modified handcuffs were given to various engineers,

technicians, law enforcement personnel, instructors and

administrators with variable knowledge of handcuffs to see if they

could open them. They tried with and without the keys. No one

was able to open the hollow swivel type in a reasonable time

period, even when not applied to a wrist. The double keyhole type

was opened by only a few (with some difficulty) as the second

keyhole gave a somewhat obvious clue as to its method of

operation, whereas, with the hollow swivel, the clue was well

j hidden. There was a general consensus that either type v^ould be

I

il very difficult to pick by a handcuffed subject. A number of those

who evaluated the double-key type believed that there v;ould be

some objection to the use of two keys to open the handcuffs,

although it was admitted there was high security due to the

I requirement of two keys used simultaneously.

I
OTHER POTENTIAL HANDCUFF IMPROVEMFNTF

During this investigation a nximber of possible handcuff

modifications, other than to the lock, were identified. These

modifications eliminate structural v;eaknesses or simplify

operational procedures and are enumerated belovr:

1. Use a single chain link instead of the present two or more.

With two chain links, it is possible to interlock the handcuff

swivels allowing the individual to stress the swivels to

failure. The use of a proper sized single chain link would

preclude interlocking the swivels

2. Add a back edge chamfer to and reduce the slope of the last

ratchet tooth to facilitate finding (in the dark) the last

ratchet tooth so that the handcuffs can be stowed in this

position (see fig. 4) . When this last tooth is engaged it

will take less time and force to apply handcuffs to a subject

reducing the chance for wrist injury or claims of wrist injury

by the subject.

3. Add coined "match-up" marks to the ratchets and housings.

This v;ill facilitate finding and stowing of the handcuffs at

the last tooth for the reasons cited in the preceding

paragraph. Such marks would make it easy to visually check if

the handcuffs were so stowed.

16
4. Use a single, heavier cheek plate to eliminate the present gap

between the two existing cheek plates. When handcuffs are

applied to an individual the gap between the cheek plates is

readily accessible and almost any available prying tool may be

engaged in the gap. Even the ratchet of the other handcuff

may be inserted into the gap and a large mechanical advantage

may be brought to bear upon the cheek plates and rivets. If a

single and necessarily stronger cheek plate is used, this gap

would not exist and the ability to pry cheek plates apart

would be eliminated. This design change would also require a

design change in the ratchet pivot point. A possible benefit

of such a change is that there could be an opportunity to

combine several parts into a single part.

5. Use a longer pusher that protrudes a small distance from the

housing when the bolt is in the inactive position such that

the pusher may push the bolt to the active position without

the use of a key tip. Present handcuffs use a short pusher

that does not extend to the housing's external surface thereby

requiring the use of the key tip or other pin-like object to

activate the double lock. This present arrangement makes it

relatively difficult for an officer to activate the double

lock once an individual is handcuffed. This becomes an

important problem if the individual is hostile or it is dark,

when it would be difficult to get the key out, find the pusher

hole, engage the pusher and press upon the pusher to activate

17
the double lock. This improvement is automatically

incorporated with the proposed automatic double/triple lock

feature as that feature requires the use of a longer pusher

and the double lock is automatically activated when the

handcuffs are properly applied. The longer pusher improvement

is listed separately since it may be incorporated

independently of the automatic double/triple lock feature. It

is important that the length of the pusher be increased only

by the minimum amount required, so that the double lock will

not inadvertently or maliciously be activated.

6. Use bags made of canvas, rubber or leather with ties to cover

the person ' s handcuffed hands thereby depriving him of the

effective use of his fingers. Under some circumstances a

handcuffed individual may be able to overpower an arresting

officer and take the officer's weapon and use this weapon to

effect an escape. Anytime that a handcuffed person has the

use of his fingers he should be viewed as a potential escapee

and still very dangerous. When each handcuffed hand is inside

a separate secure bag of stiff material the use of the fingers

is significantly impaired. Since officers presently carry a

considerable amount of special purpose equipment on their

person these bags could be carried in a convenient place in

the squad cars for ready use to enhance the security of

handcuffs aftejj the handcuffs are applied to the individual.

18
CONCLUSION

Modifications and test results have shown that with fairly

easily implemented changes it is possible to significantly

increase the security of handcuffs.
NBS-114A (REV. 0>78)

USCOMM-DC

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