We are trying to establish incoming inspection criteria for accept/reject of commercially provided nuts. There is an "urban legend" at our company that a cylindrical plug gage at the maximum minor diameter (sounds like an oxymoron!) can enter up to (or through?) the second thread and be considered acceptable. I would appreciate any guidance regarding this and sources to refer to. Thanks:thanx:

I am baffled. Are you checking these nuts with a thread plug gage? If so I would make that my criteria. If you are only checking the minor dia with a plain plug gage then I would say if the pin for the maximum minor diameter enters (no min spec) the nut then I would reject it. I am not sure if this is spelled out in any particular spec. Hope this helps.

3 turns is the max

ANSI standard BI.3M

Depending on the class of nut. That is the normal regular ol'nut.

To clarify, we are inspecting with a threaded plug gage to verify pitch, etc. but also inspecting with a plain plug gage to verify minor diameter. Thanks

Sorry for the confusion. see my additional reply.

hmm, a go / no-go is just that, if the no-go even starts then it is no good. You would need a spec for the nut to see if there is a lead in taper. There are many nut designs, some have taper lead in others do not. The chamfers, angles all are controled by the specs. Some are very tight, I have inspected aircraft landing gear screws and nuts, those are $100+ screws and have very tight tols. So refer to the actual spec for the class and type of nut.

leetimothyj-

If you check your trusty Machinery's Handbook (page 1913 in the 27th edition, look for the section Thread Gages in other editions), it quotes ANSI/ASME B1.2-1983 (R2001), Gages and Gaging for Unified Inch Srew Threads as follows:


"GO and NOT GO Plain Plug Gages for Minor Diameter of Product Internal Thread: (Recommended in Class Z tolerance.) GO plain plug gages must completely enter and pass through the length of the product without force. NOT GO cylidrical plug gage must not enter."


That said, I've generally allowed a thread or two if I was certain that I knew the application and that a slightly oversized minor Ø wouldn't cause any harm. But I also never have felt the need to inspect commercially supplied nuts so I'm thinking you must have a much more critical application than the ones I have dealt with. If that is the case, I would play it strictly by the book.

Regards -John