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Simple threading question
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Brass_Machine:
So here is a simple question(s). I have yet to thread on my lathe or really use a die that much. If I want to create say a 3/8 24 thread, what diameter should the rod be? All the tap & die charts I have found have been tap only.

Eric
Stilldrillin:
I'd say 3/8", Eric!  :thumbup:

Or, am I missing something?  :scratch:

This is the second time I've been asked that, this week......

David D
philf:
Eric,

It should nominally be 3/8".

When you measure a bolt the (outside or major) diameter is usually a little smaller (Say 0.005") than the nominal but never any bigger.

Cheers.

Phil.
Brass_Machine:
Ya know that is what I thought. Wasn't sure if it was supposed to be slightly under sized or not though. Thought I had heard it should be. Wanted to verify.

Thanks
AdeV:
Slightly undersize will make a bolt easier to fit into a corresponding nut or threaded hole, the trade-off being the fit will be a bit sloppy. There are 3 classes of fit, I believe, can't remember the names but it's basically a) flops about like cooked spaghetti, b) not difficult to screw in, but doesn't flop about so much, and c) as tight as a duck's bum - hard to do up but a very close fit.

Also, if you slightly undersize the stock, you'll find it easier to thread using a die. If you single-point it, there's no difference between undersize or full size.
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