Socket sets

If surface drive is the type with a 'bump' to contact the flat face of the hex rather than a corner, then yes. Also better for getting out bolts which have already been rounded.

Steve

Yes. If you're thinking of buying some, they are also known as 'wall drive' or 'flank drive' sockets. Or ring spanners come to that. Mike.

Would these be the type to use when trying to remove very stubborn bolts? (At the last cambelt change, I requested that the thermostat be replaced on my Astra (X reg 1.6l petrol) as the engine temperature seemed to be low, and much too variable with external ambient changes. Small garage said that they'd tried and had given up, as the bolts were so firmly stuck that they risked damaging them.) Thanks

Sadly the failure mode of those is that the bolt snaps , rather than rounding off.

They're better all round IMO. Especially for stubborn nuts or bolts. They cost quite a bit more than conventional sockets and spanners, which probably explains why they're not as widely available.

Might still not have worked for your thermostat housing bolts. IME if they're really tight, rather than undo, they break. Mike.

I's recommend them for use on *any* bolt myself, far less chance of damage to the fastener.

Aren't "impact" sockets all wall drive? If you ever think you might end up with a compressor and zip gun, you could kill two birds with one stone and get impact sockets now. I'd be lost without my zip gun now I've got one.

Snipped

Impact sockets are normally simple hexagon sockets, as opposed to the usual bi-hex type. Better than bi-hex as far as the rounding of nuts and bolts is concerned, but they still drive primarily on the corners. Wall or flank drive sockets and ring spanners are similar to hex drive ones, but in effect have the corners removed, so the pressure is put on the flat side of the nut/bolt, *before* the corner. For a wall drive socket, to round the nut off, it has to push the corner off starting from the hexagons base diameter, rather than progressively starting from the peak of the corner as in a plain hex or bi-hex socket. An area which is comparitively weak I hope you understand my explaination. Mike.

Think the main reason is a simple hex socket is stronger than the equivalent bi-hex.

Tother way round apparently, it's one of the advantages of Bi hex sockets that you can make thin walled ones more easily

Theoretically there's no difference in the strength of a hex socket compared to a bi-hex one. The thickness of material between the root of the internal 'vees' and the o/d are usually the same. The advantage of a single hex, is that to round a nut/bolt means the head must be reduced to it's core diameter or the across the flat size, but the corners can still be damaged if the nut/bolt is particularly tight. Damage which can be avoided by the use of a flank or wall drive socket or ring spanner. Impact sockets are made from tougher material than normal sockets, to reduce the chance of them shattering because of the violent hammering they receive. Mike.

I'll have to go check my impact set and see; I was pretty sure it was more than just hex drive. Sadly, it's p!ssing with rain here at the mo, so I can't be arsed to check tonight :-)