Specialist screwdriver bit?

Oh, good grief. I've just found this:

Apologies.

I'd call it a roofing bolt,not sure if you can get drivers for them, though.

Thanks. I actually stumbled on the correct term just after I posted the query. And using it, I was able to find this:

Hallelujah for magnetic drivers, real life savers especially for fiddly screws!

I think most people simply use a flat bladed screwdriver unless you need to use a powered driver because you have a lot to do.

I've done exactly that in the past but found a tendency for the blade to slip and potentially cause some damage: it would be fine if the slots didn't extend to the edge of the head of the bolt, but unfortunately they do. I don't mind buy a specialist tool for the job.

I don't mind buying one, either. Apologies.

I just use an ordinary, straight screwdriver, to screw head, then use a spanner on the nut itself.

Update:

I bought the specialist bit. It's certainly better than using a flat-bladed screwdriver but there's still a slight tendency to slip, exacerbated by the fact that the slots in the bolt heads are open-ended: if they were closed at the extreme ends in the manner of cross-head screws it would make the process of driving them home completely foolproof, though I presume it would also make the bolts considerably trickier to manufacture and therefore considerably more expensive.

The main problem is the slots are too wide & not deep enough. Whatever you use has to be kept in line with the shaft. I have, in the past, got the angle grinder out & deepened the slots slightly.

Are they not galvanised?

Almost invariably

Probably BZP (Bright Zinc Plated).

Actually, I have wondered about this...

I have assumed that BZP parts have the same protection as galvanised parts do via 'galvanic corrosion'. But is that true?

J^n

Not if you grind the plating away :-)

AFAICR 'galvanising' is just 'not very bright zinc plating'

Wonder what Google AI has to say

Ah. Galvanising is simply thicker. Ergo better. Hot dip versus electroplating.

Not so if the ground away bit isn't too big. That's the whole point if galvanic corrosion.