Colchester Triumph 2000 - Topslide Leadscrew Threadform

[Twizseven]

A quick question.

I am in need of a new topslide nut and this is going to be made by a friend on his Hardinge lathe as we need the existing leadscrew to test the nut. I have checked with Colchester Spares and the leadscrew is 5/8" diameter (0.625") and has a 2.5 pitch metric thread. I am trying to ascertain whether this is a 29 degree Imperial threadform or a 30 degree Metric threadform. None of the threadgauge sets we have possess a 2.5 pitch threadform they all go from 2 pitch to 3 pitch.  It is very hard to see a 1 degree difference.  Can anyone confirm, one way or another.

Thanks,

Colin

[BillTodd]

Is it a double start thread?  5mm lead.

Might be worth molding some epoxy filler around the screw , then remove and section to check the thread form (WAG itll be 29 because that's what tooling they had in the leadscrew machine!)