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Re: pitch diameter

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On Jul 7, 2009, at 7:47 PM, Conrad Harrison wrote:

From memory. A thread is considered a cantilever beam, with a point load applied at the middle of the span, and the section properties taken at the middle of the span. Pitch diameter is midway between the major diameter and the minor diameter.
Not quite accurate. The convention is that the bolt or screw (external thread) fails in tension at the OD of the 'stress area.' The stripping failure mechanism of the internal thread is shear across the pitch diameter. You can also calculate a load for stripping the male thread in the event that the screw or bolt is weaker than the internally threaded element. Machinery's Handbook has formulas for calculating these failure loads. You can find pdfs of federal Standard H28 on line with a quick Google search

Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw(--nospam--at)   | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania 1864)

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