June 25, 2007

Folks, we have an OEM who designed and qualified an assembly for military 
(NAVY shipboard) shock and vibration requirements via performing shock and 
vibration testing.  His qualified design used split ring lock washers.  To 
save $ (assembly time primarly), the OEM proposes to replace the split ring 
lock washers with Nylok type locking nuts.

Question is, would the OEM need to repeat the shock and vibration 
qualification testing.  My understanding is that although split-ring washers 
are sometimes called lock-washers, in fact, they do not "lock" the fasteners 
in place, as is specifically stated in the applicable MS standard/mil spec 
for the washers.  Apparently the Nylok locking nuts that have the plastic 
(nylon??) insert are true locking devices and as such perform better as a 
locking feature than do split-ring lock washers.  Therefore, there should be 
no need to repeat shock and vibration qualification testing if the OEM 
changed from split-ring lock washers to use Nylok type locking nuts.  The 
only possible concern I am aware of is that the locking nuts can only be 
used (removed and re-installed) a specified number of times (e.g., 10 to 15 
times?).

I would like any Technet folks information on the above.  Thanks.

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