Though I have numerous engineering books in the office here
I couldn't find the answer. The only answer on the web I could
come up with is 30% of the ultimate tensile stress. 
http://www.bigcee.com/reference.html He/she claims
to have data from the AIAA Design Handbook for Aerospace Engineers
of which I don't have a copy
 
YMMV
Peter van Hoof


----- Original Message ----
From: "Buehler, Martin" Martin.Buehler@keymile.com


thanx for the answer.
0.6 seems to be good for practical use.
unfortunately, i need to get the exact value for an M20 shaft screw,
with a shaft diameter of 21mm.
googling around, i wasn't able to get any info on something like that!
tino
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