John Doe wrote:

snip

Maybe I should have just asked for better machine screws without any
description, but some people prefer to know what's going on.

Okay. It would really help if you could post a picture of the two parts
and the failed screw. Then it would be much less a case of guesswork.

If you don't have any web space, e-mail the picture to me and I'll host
it for you: cdt22 AT cantabgold. DOT net

Best wishes,

Chris