British car suspension threads.(MG, Morris etc)

[zzr1200]

Big book of "Machinery's Handbook" on it's way. Meanwhile, where might I look for someone to make a one-off tap for a square profile thread?

Try "Tracey Tools" when you have worked out what thread it is, if your lucky they'll have one on the shelf. If you have to have one made they cost a fortune, I was quoted £250-00+ for a 9/16 x 5 twin start acme tap.

But someone with a lathe could possibly make the part if the correct steel grade is purchased.

 

[Seadog]

square buttress thread

It's a square thread OR a buttress thread, it can't be both. I'd be inclined to say it's square from what I can make out in the photo.

 

[rtbcomp]

IIRC the Riley ones were square