3 Wire thread measurement

[eightball]

I have an o ring set that i generally use to hold wires. On small shafts i roll up a ball of duct seal putty and stick one end of the wires in it. then i only have to hold the other end. Ive done the same thing with foam rubber but like using the puttythe best. anything over an inch i use the o rings. That frees up both my hands. And pitch diameter is the most critical deminsion on a thread. Hope this helps.