Percentage Strength of Number of Threads Engaged



To All:

Here is some validation for the old rule of thumb that 6 threads is all you need to be engaged in the work.

Best to visit the site because they have a simple graphic showing the stress on the threads.

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http://www.gizmology.net/nutsbolts.htm

As nuts and bolts are not perfectly rigid, but stretch slightly under load, the distribution of stress on the threads is not uniform. In fact, on a theoretically infinitely long bolt, the first thread takes a third of the load, the first three threads take three-quarters of the load, and the first six threads take essentially the whole load. Beyond the first six threads, the remaining threads are under essentially no load at all. Therefore, a nut or bolt with six threads acts very much like an infinitely long nut or bolt (and it's a lot cheaper).


Stress on bolt threads. Note how the majority of
the stress is on the first thread to the left.
Image from Spiralock.



Thread % %Sum
1 34% 34%
2 23% 55%
3 16% 71%
4 11% 82%
5 9% 91%
6 7% 98%

There is little point in having more than six threads in anything. Nuts with National Coarse threads typically have 5 threads in them, whereas nuts with National Fine threads have about 8 threads. Nuts are usually stronger than the bolts they are on, which is to say that the bolt will usually break before the nut strips.
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--
BottleBob
http://home.earthlink.net/~bottlbob

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