Technical data

13773-001
20-50
Page 1
SAFETYING
1. DESCRIPTION
This section contains information on the proper safetying techniques and procedures used when fastening
hardware.
2. MAINTENANCE PRACTICES
A. Safety Wiring
There are two basic forms of safety wiring. The single-wire method and the double-twist method.
Safety wire comes in three types which are identified by size and color. The three types are classified
by use. Inconel and Monel wire is used for general safety wiring and is identified by a natural wire
color. Monel can withstand temperatures up to 800°F; Inconel can withstand temperatures up to
1500°F. Copper that is cadium-plated and dyed yellow is used for shear and seal wiring applications.
Aluminum Alloy (Alclad 5056) is dyed blue and is used exclusively for safety-wiring magnesium parts.
Size of wire is dependent on material and purpose of installation. Use a 0.020” diameter copper wire
for shear and seal applications. Use a 0.020” diameter wire to safety wire parts with tie holes smaller
than 0.045” or on parts with a tie hole diameter between 0.045” and 0.062” when spacing between
parts is less than two inches or, when bolts and screws of 0.250” diameter or less are closely spaced.
Use a 0.032” diameter wire (minimum) for general purpose safety wiring.
Shear applications are those where it is necessary to break or shear wire to permit operation or actua-
tion of emergency devices. Seal applications are where wire is used with a lead seal to prevent tam-
pering or use of a device without indication.
(1) Single Wire Method (See Figure 20-501)
The single wire method has a limited application. Single-wire method is used for shear and seal
wiring applications. The single wire method is most commonly used on emergency equipment.
The single wire method is also used when a series of three or more parts, usually small screws
or bolts, are in a closely spaced geometric pattern (square, rectangle, or circle). Closely spaced
is defined as the spacing of two inches or less between the centerline of parts. The wire in this
application is strong enough to safety the part, but can be easily broken when use of the emer-
gency equipment is required. A third application of the single wire method is safetying hard to
reach parts which are impractical to double wire. Single-wire method is accomplished by passing
a single wire through tie holes and back with the ends then twisted together. Wire twisting pliers
are used to obtain a uniformly tight twist in the wire.
Note: When using single-wire method of safety wiring, the largest wire that will fit the tie
holes should be used.
(2) Double Wire Method (See Figure 20-502)
The double-twist method is the most common method of safety wiring. When double wire safety-
ing in a series, the direction of twist must be reversed at each unit. When safetying widely
spaced series using this method, the maximum number of units is three. Safety wiring by the
double-twist method is really one wire twisted on itself several times and is accomplished by
inserting one end of the wire through the tie holes of the bolt head and firmly loop around the bolt
head. This does not necessarily apply to castellated nuts when the slot is close to the top of the
nut. The wire will be more secure if it is made to pass along side of the stud. While taut, twist the
strands to within 1/8” of the next part. The twisting keeps the wires taut without overstressing
and prevents the wire from becoming nicked, kinked, or mutilated. After the last tie hole, the wire
is twisted three to five times to form a pigtail. Cut off any excess wire and bend the pigtail
towards the part.
30 Nov 2000