Lock nuts come in many different shapes and sizes with a variety of of different locking mechanisms each of which is suited for specific applications. They all function to increase the resistance to loosening forces without the use of lock washers. This has improved efficiencies and lowered costs in many manufacturing processes.
Lock nuts typically fall into one of two groups:
PREVAILING TORQUE LOCK NUTS
An intrinsic feature of the lock nut produces friction between threads of mated components resulting in increased resistance to loosening forces. Consequently, unlike free spinning lock nuts, torque must be applied during both assembly and dis-assembly - prevailing torque. The advantage of this type of nut is that loosening is unlikely even if pre-load is reduced completely because of the remaining rotational resistance. Prevailing torque lock nuts are not ideal to use with long threaded assemblies because long spans of threads may reduce the effectiveness of the nut's locking mechanism. Therefore, the length of the bolt or screw should not be much longer than that needed to ensure full thread engagement with the nut. The two main categories of prevailing torque type lock nuts include: all-metal lock nuts and nylon insert lock nuts.
SURFACE-BEARING LOCK NUTS
Free spinning nuts that require tightening against a bearing surface in order for the locking mechanism to function. If the bearing surface onto which the nut is tightened is painted or plated, localized corrosion is a possibility if wrenching the nut damages or removes the surface treatment. Because the serrations must contact the mating surface to "lock", serrated flange nuts are not used with flat or lock washers.Two common surface bearing type lock nuts include: serrated flange lock buts and KEPS nuts (K-Lock nuts).
Material, Threading and Sizes
Available threads include standard right-hand and Unified inch coarse series (UNC, Unified National Coarse) or Unified inch fine (UNF, Unified National Fine). Sizes refers to the nut's nominal thread diameter. Nut width across flats, (wrench size), and thickness vary with nut size.
Typically, sizes range from about #4 to 1". Sizes less than 1/4" are listed as a number size (the larger the number the larger the size) while sizes that are 1/4" and larger are specified in inches, usually fractional rather than decimal. Locknuts are available in mild steel, Grade 5 steel and Grade 8 alloy steel. Plating is in regular zinc, black zinc, yellow zinc and black oxide.
Stainless steel lock nuts are also available. For additional details, dimensions and specifications on lock nuts and specification
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