GENERAL INFORMATION 7 Common nut Self-locking nut Correct installation of cotter pin Wing nut Flat washers are often used between a lockwasher and a fastener to provide a smooth bearing surface. This allows the fastener to be turned easily with a tool. NOTE As much care should be given to the selec- tion and purchase of washers as that given to bolts, nuts and other fasteners. Avoid washers that are made of thin, weak materi- als. These will deform and crush the first time they are torqued, allowing the nut or bolt to loosen. Plain Folding Internal tooth External tooth Cotter Pins Cotter pins (Figure 13) are used to secure fasteners in a special location.
The threaded stud or bolt must have a hole in it. The nut or nut lock piece will have castellations around its upper edge into which the cotter pin fits to keep it from loosening. When properly installed, a cotter pin is a positive locking device. Purchase a cotter pin that will fit snugly when inserted through the nut and the mating thread part. The cotter pin should not be so tight that it has to be driven in and out, but it should not be so loose that it can move or float after it is installed. Before installing a cotter pin, tighten the nut to the rec- ommended torque specification.
Ifthe castellations in the nut do not line up with the hole in the bolt or stud, tighten the nut until alignment is achieved. Do not loosen the nut Washers There are two basic types of washers: flat washers and lockwashers. Flat washers are simple discs with a hole to fit a screw or bolt. Lockwashers are designed to prevent a fastener from working loose due to vibration, expansion and contraction. Figure 12 shows several types of wash- ers. Washers are also used in the following functions: a. As spacers. b. To prevent galling or damage of the equipment by the fastener. c. To help distribute fastener load during torquing. d. As seals.