OldScrawn wrote:
However I would have thought that at least some of the better
screw manufacturers would publish such figures.


Well, for "high tensile" bolts you can usually work out the values from the
numbers stamped on the heads. But then, you might want to know the strength of
the bolts if (say) you were using six of them to hold a 2 inch flange on a 100
psi system. But you are not usually doing stress analysis on wooden structures
held together with screws. Why were you asking? Find a friendly metallurgy lab
and you might get them to measure the hardness for a particular type of screw,
then there are formulae. Usually what you want in carpentry is a joint that is
as strong in shear as the wood. You don't need much area of the weakest steel
to get enough normal force across the joint; friction and/or glue do the rest.

As I was trying to explain in my original question I'm not in the
slightest bit interested (well, not for this question anyway) what the
*tensile* strength of screws is. So it's not about how well they hold
things together.

What I'm after is how easy it is to break them, especially with a
power screwdriver.

--
Chris Green