special washers. Figure 5-29 shows some of the most
commonly used types.
PLAIN WASHERS
Plain washers are widely used under AN hex nuts
to provide a smooth bearing surface. They act as a shim
in obtaining the correct relationship between the
threads of a bolt and the nut. They also aid in adjusting
the position of castellated nuts with respect to drilled
cotter pin holes in bolts. Plain washers are also used
under lock washers to prevent damage to surfaces of
soft material.
LOCK WASHERS
Lock washers are used whenever the self-locking
or castellated type nut is not used. Sufficient friction is
provided by the spring action of the washer to prevent
loosening of the nut because of vibration. Lock washers
must not be used as part of a fastener for primary or
secondary structures.
Star Lock Washers
The star lock or shakeproof washer is a round
washer made of hardened and tempered carbon steel,
stainless steel, or Monel. This washer can have either
internal or external teeth. Each tooth is twisted, one
edge up and one edge down. The top edge bites into the
nut or bolt and the bottom edge bites into the working
surface. It depends on spring action for its locking
feature. This washer can be used only once because the
teeth become somewhat compressed after being used.
Tab Lock Washers
Tab lock washers are round washers designed with
tabs or lips that are bent across the sides of a hex nut or
bolt to lock the nut in place. There are various methods
of securing the tab lock washer to prevent it from
turning, such as an external tab bent downward 90
degrees into a small hole in the face of the unit, an
external tab that fits a keyed bolt, or two or more tab
lock washers connected by a bar. Tab lock washers can
withstand higher heat than other methods of safetying,
and can be used safely under high vibration conditions.
Tab lock washers should be used only once because the
tab tends to crystallize when bent a second time.
SPECIAL WASHERS
Special washers such as ball seat and socket
washers and taper pin washers are designed for special
applications.
Q5-15.
Washers used in aircraft structures are
grouped into what three general classes?
SUMMARY
In this chapter you have been introduced to the
various types of aircraft hardware used in naval aircraft
and the procedures for maintaining their security. It is
essential that the correct hardware be used at all times
for the safe and efficient operation of naval aircraft.
5-20
ANF0529
PLAN
BALL SEAT
& SOCKET
TAPER PIN
SPECIAL WASHERS
TAB LOCK WASHER
STAR LOCK WASHER
Figure 5-29.—Various types of washers.
