Castle nuts are used with drilled-shank AN
hex-head bolts, clevis bolts, or studs. They are designed
to accept a cotter pin or lockwire for safetying.
Castellated shear nuts are used on such parts as
drilled clevis bolts and threaded taper pins. They are
normally subjected to shearing stress only. They must
not be used in installations where tension stresses are
encountered.
Plain hex nuts have limited use on aircraft
structures. They require an auxiliary locking device
such as a check nut or a lock washer.
Wing nuts are used where the desired tightness can
be obtained by the fingers and where the assembly is
frequently removed. Wing nuts are commonly used on
battery connections.
Self-Locking Nuts
Self-locking nuts provide tight connections that
will not loosen under vibrations. Self-locking nuts
approved for use on aircraft meet critical specifications
as to strength, corrosion resistance, and heat-resistant
temperatures. New self-locking nuts must be used each
time components are installed in critical areas
throughout the entire aircraft. Self-locking nuts are
found on all flight, engine, and fuel control linkage and
attachments.
There
are
two
general
types
of
self-locking nuts. They are the all-metal nuts and the
metal nuts with a nonmetallic insert to provide the
locking action. The Boots aircraft nut and the Flexloc
nut are examples of the all-metal type. See figure 5-7.
The elastic stop and the nonmetallic insert lock nut are
examples of the nonmetallic insert type. All-metal
self-locking nuts are constructed either of two ways.
The threads in the load-carrying portion of the nut that
is out of phase with the threads in the locking portion is
one way. The second way is with a saw-cut top portion
with a pinched-in thread. The locking action of these
types depends upon the resiliency of the metal.
5-5
ANF0507
BOOTS AIRCRAFT NUT
FLEXLOC NUT
NONMETALIC-
INSERT
LOCK NUT
ELASTIC
STOP NUT
ELASTIC TWO-LUG
ANCHOR NUT
BOOTS AIRCRAFT CHANNEL ASSEMBLY
ELASTIC STOP NUT CHANNEL ASSEMBLY
Figure 5-7.—Self-locking nuts.
