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On Sunday, September 8, 2013 2:35:56 AM UTC-4, Howard Beal wrote:
A common internal thread, drilled so that it results in 50% of full
thread
will break the external thread, before the internal thread will
strip.
Tom.

If I recall correctly that is true for holes that the engagement
length is at least as long as the diameter.
Dan

I distantly remember from college that the minimum engagement length
was a good rule of thumb to apply if you didn't have data on the
material properties. Later I heard it in auto and aircraft contexts.

A Grade 8 screw in an aluminum casting won't fail the same way as a
Grade 2 in a steel nut, and coarse threads are more likely to break at
the thread root, fine ones more likely to strip. If we knew the
properties we were supposed to calculate how much the male element
would stretch and IIRC design so the threads fail by stripping
progressively, beginning at the hole surface where bolt stretch is
greatest.

Herreshoff designed his rigging turnbuckles such that the barrel and
eyebolts stretched identically. When tested to failure all parts
deformed before any broke.

The college class was for chemists and perhaps not as extensive in
mechanical failure modes as one for MEs, but it went far into
alloying, grain structure and corrosion.

jsw