I do a lot of repair and custom work on electric lighting. This includes
retrofitting European lamps to American sockets and wiring.

Here in the states, the threading and sizes on our lamp piping is all based
on gas piping since our electric lamp industry evolved from our gas light
industry.

On the European lamps (mostly British and French) there is a thread I have
never been able to figure out.

It appears to be about 19tpi (or perhaps 1.33mm) and runs around .415 in.
outside dia (or perhaps 10.5mm).

It doesn't seem to match anything.

I made myself a tap several years ago, but it is wearing out and I would
love to find a real tap for it. Unfortunately I don't even know what size to
look for.

Any help would be greatly appreciated.

Paul K. Dickman