Thread measurement

[prophet455]

I am looking for a standard in thread measurement. When a print calls for 8mm min of thread it would seem reasonable that they mean 8mm of full depth thread, however where is the standard that says it is full depth only?

[Ed Hume]

If you cannot easily find a standard, it doesn't matter whether there is one or not since you cannot assume the designer saw the standard either. So you go back to the designer's intention - and any good designer has allowed some tolerance for the fit of the mating part. If you are making the part for yourself, it is reasonable to screw on a nut and validate that the nut can go on 8mm. If you are making the parts commercially, then I believe the golden rule supersedes all applicable standards - he that has the gold, makes the rules.

[Ed Hume]

Prophet455,

My earlier answer was meant to be an amusing way of bringing up the Golden Rule joke, but your post deserves a better reply than that. I looked up the subject in a classic reference, Fundamentals of Engineering Drawing eight edition by Luzadder. I got this book dirt cheap 2nd hand because it predates the CAD era. Here is what the text says:

"14.18 Thread Dimensioning. In general, the
thread length dimension shown on a
drawing should be the length of the complete
(full-form) threads. The incomplete
threads should be beyond this dimensioned
length."

So your assumption is correct, a drawing dimension is usually for full form threads, and this appears to be common knowledge - something that is probably specified in an ANSI or ISO standard that pertains to drawings.

Best regards,
Ed

[Russells]

The current rule of law in the US is :ASME B1.1 and ASME B1.13 for metric threads. This superseded ANSI B1.1 And 1.13, which superseded FED-STD H28 for threads. The bottom line is that the thread is measured where it is fully formed. partially formed threads are usually referred to as thread run-out .

Russells

[prophet455]

Thanks guys this is what I thought. Of course this is a commercial application or it would be easy to fix.