Hi Alan
I like the casual way you say 20tpi tap
It does sound like a good plan though to make longer collars, so long as I can find a suitable tap !
If only you were a bit closer and I'd post you a length of tube to tap for me
- I've got an old bent commando fork tube that might do, or if not that, several velocette ones (I race them).
Everything I've done with motorbikes this year has started well than taken a quick turn into a hidden ditch
phil