threads have not been damaged. If the locking
material has not been damaged or permanently
distorted, it can be reused.
NOTE: If any doubt exists about the
condition of a nut, use a new one!
Installation of Nuts and Bolts
It is of extreme importance to use like bolts
in replacement. In every case, refer to the
applicable maintenance instruction manual and
illustrated parts breakdown. Be certain that each
bolt is of the correct material, size, and grip
length. Examine the markings on the head to
determine whether a bolt is steel or aluminum
alloy. This knowledge is especially important if
you are to use the bolt in the engine hot section.
Use washers under the heads of both bolts and
nuts unless their omission is specified. A washer
guards against mechanical damage to the material
being bolted. A washer also prevents corrosion
Figure 2-19.--Various types of washers.
of the structural members. An aluminum alloy
washer used under the head and nut of a steel bolt
securing aluminum alloy or magnesium alloy
Sufficient friction is provided by the spring
members will corrode the washer rather than the
action of the washer to prevent loosening of the
members. Steel washers should be used when
nut because of vibration. Lock washers must not
joining steel members with steel bolts.
be used as part of a fastener for primary or
Whenever possible, the bolt should be placed
secondary structures.
with the head on top or in the forward position.
This positioning helps prevent the bolt from
The star lock or shakeproof washer is a round
slipping out if the nut is accidentally lost.
washer made of hardened and tempered carbon
steel, stainless steel, or Monel. This washer can
WASHERS
have either internal or external teeth. Each tooth
is twisted, one edge up and one edge down. The
Washers used in aircraft structures may be
top edge bites into the nut or bolt, and the bottom
grouped into three general classes: plain, lock
edge bites into the working surface. It depends
washers, and special washers. Figure 2-19 shows
on spring action for its locking feature. This
some of the most commonly used types.
washer can be used only once because the teeth
become compressed after being used.
Plain Washers
Tab lock washers are round washers designed
with tabs or lips that are bent across the sides of
Plain washers are widely used under AN hex
a hex nut or bolt to lock the nut in place. There
nuts to provide a smooth bearing surface. They
are various methods of securing the tab lock
act as a shim in obtaining the correct relationship
washer to prevent it from turning. An external
between the threads of a bolt and the nut. They
tab bent downward 90 degrees into a small hole
also aid in adjusting the position of castellated
in the face of the unit, an external tab that fits
nuts with respect to drilled cotter pin holes in
a keyed bolt, or two or more tab lock washers
bolts. Plain washers are also used under lock
connected by a bar are some of the present
washers to prevent damage to surfaces of soft
methods used. Tab lock washers can withstand
material.
higher heat than other methods of safetying. The
washer can be used safely under high vibration
Lock Washers
conditions. Use tab lock washers only once
Lock washers are used whenever the self-
because the tab tends to crystallize when bent a
locking or castellated-type nut is not used.
second time.
2-15
