John Doe wrote:
Like by ignoring the question and for some strange reason insisting
that threading a machine screw into a properly tapped hole is the
only valid application for a machine screw. Plastic screws into
properly tapped holes. Threading screws into a hole is not the end
objective. The objective is to keep the pieces together. I can tell
that the bolts aren't strong enough, that's why I ask for better.
The point here is that if the screw is binding in the thread,
and requires more than a twist of the finger to put it in with
NO load, it will bind a LOT WORSE under axial load. This is
probably the MOST common failure mode of a screw or bolt. The
thread binds up to the point that the shank fails in torsion,
not from axial tension.

Without knowing more about what size bolt/screw, what kind of
tension you are trying to achieve, what alloy and how much
thread engagement there is, it is REAL hard to advise further.
If you need 1000 Lbs of axial force out of a 6-32 screw, you
need to go up a couple sizes. If a 1/2-13 is breaking off at
only 1000 Lbs axial load, you have to be doing something wrong,
or the bolts are made out of recycled beer cans.

Jon