Dan Gravell wrote in message ...
Hi there,

I have a very small allen key screw which screws into the bottom of my
shower mixer unit to fasten the thermostat and control to the shower.



You could try those "star" ended screwdriver bits & hammer it in but
you might do damage to where the screw fits in.

You could drill it out - you've already got a pilot hole of sorts. A
reverse drill would be better but you could just drill through then
pick out the remainder.