Understanding AN Hardware Nuts And Bolts
Various types of AN screws and nuts are used in the construction of aircraft. In order to properly design and build an aircraft one must have a good working knowledge of the AN hardware and its applications. AN500 (coarse thread) & AN501 (fine thread) Filister head screws are available in various thread sizes from 4-40 to 1/4-20 and lengths from 5/16 to 1 inch. Tensile strength is 55,000 PSI. AN502 & 503 Fillister head screws have drilled heads to accommodate safety wire and have a higher tensile strength (125,000 PSI). Thread sizes are 10-32 and 1/4-28.
MS24693 (formerly AN507) non-structural machine screws have a 100 degree countersunk flat head and are rated at 55,000 PSI. The lengths vary from 3/8 to 2 inch and thread sizes range from 4-40 to 1/4-28.
High strength MS24694 machine screws (formerly AN509) should be used in structural applications. The minimum tensile strength is rated at 125,000 PSI. Structural machine screws are normally used with self locking castle or stop nuts and AN960 flat washers or thin check nuts and lock washers. Sizes range from 8-32 to 5/16-24. Lengths are available from 9/32 to 2-7/8 inches and grip lengths range from 7/16 to 9/16. The sheet material being fastened with machine screws should be thick enough to accommodate the countersunk head.
When fastening thinner sheet material AN525 Washer head screws should be used. Washer head screws are rated at 125,000 PSI. Thread sizes are available from 8-32 to 1/4-28. Washer head screws should be secured with locking nuts and washers.
AN310 castle nuts are used with drilled shank bolts, clevis bolts, eye bolts, and studs. The slots in the nuts will accommodate a cotter pin for safety purposes. Thread sizes vary from 10-32 to 3/4-16.
The thinner castlellated AN320 shear nuts are used with clevis bolts and threaded taper pons and have half the tensile strength of the AN310 nut. AN320 nuts are used in applications where only shear loads are experienced.
MS 17825 self locking castle nuts have a nylon insert for added safety and are useful for securing control systems since the nylon insert will act as a stop nut in case the cotter pin should break. AN 315 hex nuts have the same strength as castle nuts but an auxiliary locking device such as a lock washer or check nut must be used for proper safety.
AN316 thin check nust are rated at half the tensile load of the AN315 hex nut. They are used as a locking nut for plain nuts. AN363 and MS21042 metal slop nuts are designed for high temperature applications. The shorter MS21042 nuts have the same tensile strength as their AN363 counterparts. AN364 elastic stop nuts have a nylon insert which provides a friction grip on the threads.
Commonly referred to as “Nylock” nuts. AN364 stop nuts and their thinner counterpart, AN365 are used for both tensile and sheer applications. Thread sizes range from 4-40 to 5/16-24. We have only covered a small portion of the available screws and nuts available for aircraft construction. For more detailed information on aircraft AN hardware you can purchase a catalog from Aircraft Spruce and Specialty or Wicks Aircraft Supply.
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