TPI in metric? And a few other leadscrew confusions for newbie

[Neale]

No, it will be labeled as 12mm, 3-start or 6mm, 2-start or whatever. Not 4mm or 3mm.

Problem is that you should really talk about "lead", which is the amount a nut would move for one turn of the screw, and "pitch", which is the distance between adjacent crests on the thread. But most of the time we tend to say pitch instead of lead, hence the ambiguity.

[glynster]

Excellent, I think I am finally understanding, so to confirm then this product from Moore International is 10mm diameter will advance by 12mm with every turn (approx half an inch)?...

http://www.mooreinternational.co.uk/...0-12screw.html

Does the nut also have to match the 12mm pitch?

[Neale]

Yes, that's a 12mm effective pitch (=lead) 4-start thread. And yes, you need the matching nut. There appears to be a dropdown box to choose Delrin or bronze for that.