What are these screw heads?

Probably Torx

Torx

HTH

Avpx

e-torx?

Thanks - yes I see now it says T-20 on the bit I was using.

Have you not encountered those before? They're frightfully common. Slightliy less common are the security version which has a hollow head with a centre pin. Not as effective as they used to be since the Chinese began making keys for them in millions.

Not as wood screws in a gate. I was quite surprised to discover that I owned driver bits for them, though. Buggered if I know when, or why, I have these. Still, useful today though. The screws are, however, rusty so I'll prolly replace them.

I had to replace the thermal cut out on my tumble dryer. I had to take the thing to pieces, and ALL the screws were T20, which I thought was very sensible and convenient.

Certainly an unusual choice from years ago, but torx woodscrews are quite common now - Screwfix sell them.

Probably a better option now than Pozi or Phillips - no cam-out on difficult to remove screws.

Yes, having read up on them and finding I have the corresponding driver bits I'll prolly replace using them.

Really quite surprised you've not come across them before, as they're pretty old. Have some on an '85 car. I like them. I reckon they 'stick' on the driver better than any other head - for replacing one in a recess, etc.

speshly on Vauxhalls...centre pins are the security version

Sounds like TORX ... been used on cras for decades, now becoming popular on wood screws .... I did a big decking project all fitted with Torx head screws. Hold & drive much better than pozi or phillips

These SPAX decking screws are the Muts Nuts .... reverse thread at top pulls decking boards down tight.

Bill

Might be some confusion with *distance screws* where gripper rings under the screw head can be used to adjust the position of a board or batten. Particularly useful where battens/boards are being fixed over foam insulation.

The deck screws are threaded from the tip to e.g. halfway along the shank, then there's a plain section, then the thread restarts again and continues to the head.

But the top section of thread is in the same direction, not reversed.