Using a die

Standard 3/4" rod...simply.

Nominally, 3/4", just as your intuition says. However, if you want it to thread a little more easily, you might shave it down to 0.745" or so. Yes, this is "cheating" but I've done this many times on larger threads if the fit isn't gnat's ass critical. Makes everything go a lot easier.

GWE

Thanks everyone.

I measured a bolt and it was about .72 -ish beneath the threads.

So that's why I wanted to make sure.

A general expression for the size of a rod for threading is: " Major diameter minus (.10825 / # of threads per inch)"

In the case of a 3/4 - 16 it would be: 0.750 - (.10825 / 16) = 0.7432

This would "cut" a class 3A thread, approximately. It might also result in die damage if cutting hard material such as stainless or etc. Check Machinery's Handbook for tables of allowances and max - min major diameters for classes of threads.

Bob Swinney

Not sure I'd use that as a guide, as many bolts today have rolled threads. That close to full diameter, though, they are probably cut.

John Martin

The standard thread strengths are base on 75% full thread. Look in Machinery's Hanbook. ERS

Well, lets say it *could* yield a class three thread, but that has little to do with the major diameter. Class of fit is controlled by the pitch diameter, which, from class to class, is very close to identical, but not necessarily identical. Each of the classes can share the same major diameter, so you can't discern a class fit by that measurement. As you and I have discussed before, the critical dimensions on screw threads are always the pitch diameters, although all features must be within specs for a proper thread.

Harold

Right, Harold. He was asking about threading with a die, so I gave the best advice under the circumstances . . . I think.