It is called a "clutch" head. The size you need is (I think)5/32 inch.
bill
25 ft Trade Wind in WV
> The small screws or bolts that hold the awning window gear housing in place
> have a head for which I cannot find a driver. It looks a bit like an
> hourglass. What is this kind of head called, and when can I find a driver for
> it?