Gear Boss

[funk2monk]

I’m restoring - slowly my 1949 Claud Butler closed circuit bike. So far so good. However I’m putting a new gear change lever onto the boss on the frame. The threaded retaining screw from the donor clamp on bracket isn’t the same thread as the boss?
Does anyone know what thread this could be please?

 

[Cycleops]

Likely an old imperial thread but easy enough to re tap it.