FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 7. Aircraft Hardware, Control Cables, and Turnbuckles | 4. Nuts | 7-63. General
9/8/98
SECTION 4. NUTS
AC 43.13-1B
7-63. GENERAL. Aircraft nuts are avail-
able in a variety of shapes, sizes, and material
strengths. The types of nuts used in aircraft
structures include castle nuts, shear nuts, plain
nuts, light hex nuts, checknuts, wingnuts, and
sheet spring nuts. Many are available in either
self-locking or nonself-locking style. Typical
nut types are shown in table 7-13. Refer to the
aircraft manufacturer’s structural repair man-
ual, the manufacturer’s engineering depart-
ment, or the FAA, before replacing any nut
with any other type.
7-64. SELF-LOCKING NUTS. These nuts
are acceptable for use on certificated aircraft
subject to the aircraft manufacturer’s recom-
mended practice sheets or specifications. Two
types of self-locking nuts are currently in use,
the all-metal type, and the fiber or nylon type.
a. DO NOT use self-locking nuts on parts
subject to rotation.
b. Self-locking castellated nuts with
cotter pins or lockwire may be used in any
system.
c. Self-locking nuts should not be used
with bolts or screws on turbine engine air-
planes in locations where the loose nut, bolt,
washer, or screw could fall or be drawn into
the engine air intake scoop.
e. Metal locknuts are constructed with
either the threads in the locking insert, out-of-
round with the load-carrying section, or with a
saw-cut insert with a pinched-in thread in the
locking section. The locking action of the all-
metal nut depends upon the resiliency of the
metal when the locking section and load-
carrying section are engaged by screw threads.
Metal locknuts are primarily used in high tem-
perature areas.
f. Fiber or nylon locknuts are con-
structed with an unthreaded fiber or nylon
locking insert held securely in place. The fiber
or nylon insert provides the locking action be-
cause it has a smaller diameter than the nut.
Fiber or nylon self-locking nuts are not in-
stalled in areas where temperatures exceed
250 °F. After the nut has been tightened, make
sure the bolt or stud has at least one thread
showing past the nut. DO NOT reuse a fiber
or nylon locknut, if the nut cannot meet the
minimum prevailing torque values. (See ta-
ble 7-2.)
g. Self-locking nut plates are produced in
a variety of forms and materials for riveting or
welding to aircraft structures or parts. Certain
applications require the installation of self-
locking nuts in channel arrangement permit-
ting the attachment of many nuts in a row with
only a few rivets.
d. Self-locking nuts should not be used
with bolts, screws, or studs to attach access
panels or doors, or to assemble any parts that
are routinely disassembled before, or after each
flight. They may be used with anti-friction
bearings and control pulleys, provided the in-
ner race of the bearing is secured to the sup-
porting structure by the nut and bolt.
7-65. NUT IDENTIFICATION FIN-
ISHES. Several types of finishes are used on
self-locking nuts. The particular type of finish
is dependent on the application and tempera-
ture requirement. The most commonly used
finishes are described briefly as follows.
Par 7-63
Page 7-11