On Tue, 26 Feb 2008 06:02:23 GMT, John Doe
wrote:

Jim Levie wrote:

Any steel screw will have greater strength than the aluminum they
are threaded into. If you are twisting the head off I'd agree with
previous posters that there's a problem with the threads in the
aluminum or that you are over toqueing the screw.

Would you agree that a harder/stronger higher grade bolt takes more
torque to break?

Absolutely the higher grade screws will be stronger than the
ungraded "mystery metal" screws at the local hardware store - but on
small #6 and #8 screws you can easily surpass the breaking strength of
even the highest grades with a hand screwdriver and a "Don't know my
own strength!" wrist. Been there, Done that, Have the T-Shirt.

Too much torque is still too much torque. If you get too good of
screws that will take being over-torqued without failure, you'll just
start pulling the threads out of the aluminum fitment they are screwed
into.

They do make torque screwdrivers that click when you reach the
proper setting. If you can't feel when it's tight, you might want to
invest in one.

And there are design limits for screws - if the assembly isn't
strong enough a "super screw" isn't going to buy you much. You need
to increase the screw size, use multiple screws, or redesign so that a
bracket or tab takes the load, and it's not all on a screw in tension.

-- Bruce --