As their name implies, selflocking nuts need no auxiliary means of safetying but have a safetying feature included as an integral part of their construction. Many types of selflocking nuts have been designed and their use has become quite widespread. Common applications are: (1) Attachment of antifriction bearings and control pulleys; (2) Attachment of accessories, anchor nuts around inspection holes and small tank installation openings; and (3) Attachment of rocker box covers and exhaust stacks. Selflocking nuts are acceptable for use on certificated aircraft subject to the restrictions of the manufacturer.
Selflocking nuts are used on aircraft to provide tight connections which will not shake loose under severe vibration. Do not use selflocking nuts at joints which subject either the nut or bolt to rotation. They may be used with antifriction bearings and control pulleys, provided the inner race of the bearing is clamped to the supporting structure by the nut and bolt. Plates must be attached to the structure in a positive manner to eliminate rotation or misalignment when tightening the bolts or screws.
The two general types of selflocking nuts currently in use are the all metal type and the fiber lock type. For the sake of simplicity, only three typical kinds of selflocking nuts are considered in this handbook: The Boots selflocking and the stainless steel selflocking nuts, representing the all metal types; and the elastic stop nut, representing the fiber insert type.