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RE: Thread shear

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Per Fastener Design Manual by Barrett, NASA Ref Pub 1228:
P = (Pi * dm * Fs * L)*(1/3)
P = Pullout load, lb
dm = mean diameter of threaded hole, in.
Fs = material ult or yield shear stress
L = length of thread engagement, in.
The 1/3 factor is empirical and allows for a degree of mismatch.  If threads
were perfectly mated the factor would be 1/2.
Harold Sprague
The Neenan Company 

-----Original Message-----
From: Robert Rollo [mailto:rrollo(--nospam--at)]
Sent: Monday, May 10, 1999 11:05 AM
To: seaint(--nospam--at); structx(--nospam--at)
Subject: Thread shear

help ! 

what length of thread is required to develop the full tension of a grade 5
bolt (3/8" diam specifically). 
is this a simple rule of thumb or must one figure the total shear plane
area, etc etc? 


robert d. rollo, PE 
Corporate Associate 
Parkhill, Smith & Cooper, Inc. 
Lubbock, Texas 
(806) 761-7539vox 
(806) 747-7146 fax