Technical data

13773-001
20-70
Page 10 30 Nov 2000
F. Washers
Do not use washers under the head of flush screws unless specifically called out. When installing a
countersunk MS20002 washer under the head of bolts, the washer shall be installed so that the coun-
tersunk side faces the bolt head. A maximum of two AN960 (thick or thin) washers may be used under
a nut on all bolts, except when a AN 970 washer is specified; then a maximum of only one additional
AN960 washer may be used between the nut and AN970 washer. A maximum of one AN960 (thick or
thin) washer may be used under the head of a bolt, except when a countersunk MS20002 washer or a
AN970 washer is specified, in which case no additional washers are allowed.
G. Lockwashers
(1) Lockwasher Usage
(a) When loosening of threaded parts would not endanger safety of airplane or people.
(b) When the self-locking feature cannot be provided in externally or internally threaded parts.
(c) When safety wire cannot be used to prevent loosening of threaded parts.
(d) When a cotter pin cannot be used to prevent rotation of internal threads with respect to
external threads.
(e) When fastening is not used for fabrication of primary structure.
(f) When corrosion encouraged by gouging aluminum or magnesium alloys by edges of teeth
on tooth-locked washers would not cause malfunctioning of parts being fastened together.