In Carroll Smith's Nuts, Bolts, Fastners and Plumbing Handbook - pg 104:
Nylon collar elastic stop nut
The most common (and least expensive) of the self-locking nuts
utilizes a nylon locking collar. It is available either as an AN/MS
item or as an industrial part. You can be certain of the material,
design and quality control on the AN/MS parts. The inside diameter
or I.D. of the nylon insert is slightly smaller than the major
diameter of the bolt thread. The nut will spin freely on the bolt
until the bolt threads engage the locking collar where they impress
(but do not cut) mating threads in the nylon. This compression
forces the upper flanks of the nut threads into metal-to-metal
contact with the lower flanks of the mating bolt threads, forming a
friction hold. This hold, combined with the compression of the
nylon, is sufficient to ensure that a properly tightened nut will
not loosen on the bolt at temperatures up to 250 degreesFahrenheit;
above that temperature the nylon loses its elasticity.
Nylon collar elastic stop nuts cannot harm the bolt threads,
are reusable many times and are also available as castellaed nuts.
They are manufactured to AN specs as AN-365 (MS20045) full-height
tension nuts and as AN-364 (MS20064) 1/2 high, or thin, shear nuts.
They are also manufactured as commercial units. I use the AN variety.
So, it sounds like these are a good thing. Interesting, because when
you read about locking systems (such as washers) Carrol Smith has few
good things to say about the commonly used systems.
Phil Bates
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