Can anyone give me a source for such a small allen key, preferably in UK, but postage from anywhere else isn't going to be a problem ?
I've tried Google with no luck so far, but I'm still looking.
The grub screw is holding an articulated mirror arm on the sharplan laser I've just aquired. I would like to rebuild that part if possible, mounting the mirrors on the xy axis of the greybeard cnc mk 2 :D

We made our own about that size when we were racing R/C cars.

Simple 5C collet indexer plus drill rod and surface grinder made keys much stronger than anything we could buy.

If you make your own on a machine, don't forget to keep it cool.

Personally, I would use piano wire and a hand file. Start with the right diamater, then work carefully, it shouldn't take more than 10 minutes.

Thanks guys, I guess that's the way I'll have to go.

Rs sell a nice set 0.5 to 5 mm