What the heck kind of terminal screw is this?!

[paulca]

I thought these were just so you could use either a flat terminal screw driver or a generic "cross" head.

Nope

It's interesting because these screws appeared in almost every single UK plug for the main screw and the wire clamp until the early 2000s before all appliances sold were required by regulation to have a molded fitted plug as standard.  They always have a full width flat slot and a smaller width cross.    Although some only had a slot it.

Whether their design intent was to allow both cross/star screw drivers or flat head screwdrives, or they were a special screw bit, the former types of screw driver both work in there and I can guarantee you that 99.999% of households use either a flat or cross bit to open plugs.

[JayMan07]

Just a quick update.  I ordered the slotted phillips #1 and the slotted pozi #1.  I filed them both down to fit the screws better.  The slotted pozi worked best, but the klein I was using originally was a very close second.  I think as of now there is really no perfect screwdriver for these terminal screws and if you look really closely at them I think they were actually designed to cause a screw driver to slip, maybe to prevent over tightening.  Even the part of the screw that is a flathead doesn't have walls that are 90 degrees.  There is a slight angle to them like this \_/ and it causes the flat head to slip after a certain amount of torque.  In short, these screws are just total garbage and I think I made a little progress, but mostly I just have to accept the fact that they are garbage. 

[system24seven]

Wera makes them, all the guys who I work with in entertainment have the Kraftform Kompact sets that include this driver in two sizes as 1000v rated.

 http://products.wera.de/en/screwdrivers_kraftform_plus__series_100_vde_165_i_pz_s_vde.html

[JayMan07]

Can you elaborate on what exact driver it is that Wera makes for these screws.  The link just took me to the Wera home page.  If it's just a slotted pozi or something like that I would say it probably isn't any better than the wiha drivers.  These screws are very very unique and I think someone would have to exactly make the driver to fit the screw because a slotted phillips and slotted pozi just don't fit very well.