LOCK WASHERS

special washers. Figure 5-29 shows some of the most commonly used types. PLAIN WASHERS Plain washers are widely used under AN hex nuts to provide a smooth bearing surface. They act as a shim in obtaining the correct relationship between the threads of a bolt and the nut. They also aid in adjusting the position of castellated nuts with respect to drilled cotter pin holes in bolts. Plain washers are also used under lock washers to prevent damage to surfaces of soft material. LOCK WASHERS Lock washers are used whenever the self-locking or castellated type nut is not used. Sufficient friction is provided by the spring action of the washer to prevent loosening of the nut because of vibration. Lock washers must not be used as part of a fastener for primary or secondary structures. Star Lock Washers The star lock or shakeproof washer is a round washer made of hardened and tempered carbon steel, stainless steel, or Monel. This washer can have either internal or external teeth. Each tooth is twisted, one edge up and one edge down. The top edge bites into the nut or bolt and the bottom edge bites into the working surface. It depends on spring action for its locking feature. This washer can be used only once because the teeth become somewhat compressed after being used. Tab Lock Washers Tab lock washers are round washers designed with tabs or lips that are bent across the sides of a hex nut or bolt to lock the nut in place. There are various methods of securing the tab lock washer to prevent it from turning, such as an external tab bent downward 90 degrees into a small hole in the face of the unit, an external tab that fits a keyed bolt, or two or more tab lock washers connected by a bar. Tab lock washers can withstand higher heat than other methods of safetying, and can be used safely under high vibration conditions. Tab lock washers should be used only once because the tab tends to crystallize when bent a second time. SPECIAL WASHERS Special washers such as ball seat and socket washers and taper pin washers are designed for special applications. Q5-15. Washers used in aircraft structures are grouped into what three general classes? SUMMARY In this chapter you have been introduced to the various types of aircraft hardware used in naval aircraft and the procedures for maintaining their security. It is essential that the correct hardware be used at all times for the safe and efficient operation of naval aircraft. 5-20 ANF0529 PLAN BALL SEAT & SOCKET TAPER PIN SPECIAL WASHERS TAB LOCK WASHER STAR LOCK WASHER Figure 5-29.—Various types of washers.