Effective Thread Length, Top Lock Nut - Inspection Techniques

D

Denden

#1
Is the acceptance of a prevailing-torque or elliptical offset (top-lock) Nut using a GO gage determined by the GO gage engaging only a single full turn of the Nut, and not significantly more just as a GO gage would have to go all the way through for a conventional (non-lock) Nut?

My 9/16-18 UNF-3B Hex Flange Nut's supplier's contention is that this Nut (with a total of ten to eleven threads) would only have to accommodate the GO gage by only a single full turn at the thread start end opposite the deformed top end to be acceptable, somehow allowing thread deformation for the locking portion to take up, what I believe to be limited to about only three, practically the entire thread length except for one just to start the thread--negating the class 3 fit specification.

Thanks!
 
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apestate

Quite Involved in Discussions
#2
I thought this was an interesting question. As no one has taken it up, here's a *bump*

So, I looked through Assist online and couldn't find a MIL standard for Top Lock Nuts. Maybe SAE?

Wikipedia agrees with the OP, but the reference is McMaster Carr catalog.
 
Y

Yooperdean

#3
You can check out Industrial Fasteners Institute standards IFI-124 (inch) or IFI-524 (metric) for a specification for the threads on locking fasteners. In section 3.2.2 they say the threads shall assembly a minimum of one full turn by fingers into any mating internally threaded component that has threads acceptable to Gaging System 21.
 
S

Sturmkind

#4
Denden;

Let us know the final resulotion to this!

A caution, though, is that elliptical prevailing torque features can become too small. We recently had an experience with an OEM who cross-threaded their bolt into a clipnut with an elliptical PT feature.

Upon examination it was evident that:
A) The ellipse was over-formed making it almost impossible to start the bolt.
B) Thread forms were excessively mis-shapen from a dull tap and incorrect feed (probably a worn clutch in the tapping head).

Thanks for introducing the question!
 
D

Denden

#5
Yooperdean,

I also have the April 1, 2002 IFI 100/107 information but "Thread Form" 5.2.2 refers only to threads having to meet ASME B1.1 without further addressing thread length of either the effective length and the deformed thread length AND "Thread Start" 5.2.3 just is as it says, referring to just starting the nut. Besides, further sampling of Nuts in dispute did reveal a significant quantity not even allowing the gage to engage a full thread as 5.2.3 states leading me to take a closer look at the threads in question and findings suggest the same as those that Sturmkind above has had experience with.

Sturmkind,

Thanks. We are observing thus far just poor workmanship here with our samples.

What would really settle effective thread length or length limitations to the deformed section (this despite the fact that we are now rejecting the parts for not even meeting the IFI single-thread engagement statement) is a standard which would clearly define this but I just have not had success since; looking into MIL and NAS standards if there is anything there to relate to. Nuts in dispute, by the way, are for military applications however not necessarily defined by the MIL standard.

Will sure update this thread of any conclusion.

Thanks again, everyone.
 
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