If you have a friend with a screwcutting lathe I would give it to them to re-cut to just above size and finish with very fine cuts and test between each cut. They can pick up the original thread near the shoulder and work from that. As the end of the thread is damaged I would be wary of using a die ...

Apologies for joining the conversation a bit late! The picture in the OP is a Croft, if I recall correctly it had a 5CWT capacity and a 350cc JAP engine. I think it was a little earlier than the Fleet.

Dave.

In reply to your original question, the Pixie did have a horn. It was A.C. and I think it was described as an A.C. Buzzer. It was mounted in the rectangular plate you mentioned that was bolted top to bottom in the inside of the frame between the headlamp and steering column. Small, round and quite ...