G'Day Wayne
The secret with the tight screws

I know what your thinking "Cherry Plucker" is WD40 then let it sit for an hour or so then give it a couple of slight quick taps, if the head snaps drill it out with a good quality stainless drill, it must be smaller in diametre or you will strip the thread, but before you start drilling use a product called TAP MAGIC it makes the steel easier to drill and saves the life of your drill bit. See link below.
http://www.tapmagic.com/TMprotap.htm
Regards
James