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Keps nuts are hex nuts with captive (non-removable) free-spinning lock washers, which are often external tooth. The nut turns freely during installation until the lock washer contacts and bites into the mating surface as the nut is tightened. If the mating surface is painted or plated, corrosion can occur if the lock washer penetrates and removes the surface treatment. Used in commercial and industrial applications, Keps nuts are also known as:
captive washer lock nuts, Keps lock nuts, K-Lock nuts.
Since they are not prevailing torque type lock nuts, they are not "locked" until fully seated and tightened.
Threads are standard right-hand and Unified inch coarse series (UNC, Unified National Coarse) or Unified inch fine (UNF, Unified National Fine).
Keps nut size refers to its nominal thread diameter. Typically, sizes range from about #4 to 3/8". 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.
Nut width across flats, which is wrench size, and thickness vary with the size of the Keps nut.
Steel, zinc plated, is a common material and finish.
Keps nuts are popular because they are low cost, reusable and the one-piece solution saves time over installing a separate lock washer and nut. However, if either the nut or washer is damaged, both must be replaced. Since they are not prevailing torque type lock nuts, they are suitable for use on long threaded assemblies and will not gall mating threads.