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How to 2-1/2" 3 LH Acme, tap??


Hot Rolled
Apr 22, 2016
San Antonio
Those inserts are for 6-pitch thread. You will have to go up to a 4L3 to cut a 3-pitch thread. Which takes a different bar that holds a no. 4 insert.
Matt, you didn't mention you had any big boring bars back when you were selling goodies!!! Or did you and I flat miss it.
thanks for the pointers Ken, this stuff is so far out of my wheelhouse that I wouldn't know one way or another :)

These bars and a bunch of others are from a relatively recent auction, a small manual job shop with a couple of 17" lathes. Send me a text and I'll send you some pics.


Jun 28, 2012
Mt Clemens, Michigan 48035
looks like the bought app has the helix angle.,, But that is easy to figure, or draw it and check with a hand protractor. Is the bought app only for sub-acme threads?

*RE: Do get the machine name because that may be a common repair part for other oil companies.
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Cast Iron
Jun 21, 2019
Hasn't shown up with the part yet, customer went silent even with parts in progress on the floor. My guess is they're busy with other breakdowns ( I hear they're having quite a few) I'll post an update when available.

Of course it doesn't help that I haven't been able to get to the shop since Monday on account of the storm here. And it's supposed to last through tomorrow now! Yikes!

Thanks for checking in on this.