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Can I use a tap and die set to change screw threads? I'm having difficulty finding the right size of screws for my project, and wish to manufacture my own. Can any type of screws / bolts be used with a tap and die kit in this manner, or do they have to be made of a specific material?

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  • P.S. Please tag this tap-and-die.
    – leeand00
    Commented Mar 23, 2015 at 16:13
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    Please try to be clearer about what you are actually doing or trying to do.
    – Ecnerwal
    Commented Mar 23, 2015 at 16:19
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    Utterly the wrong approach, as @FreeMan has answered. I know darn well what a tap and die set is, I just found your intended misuse baffling. Now clarified, but still baffling.
    – Ecnerwal
    Commented Mar 23, 2015 at 16:34
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    Metric screws are dead easy to come by. The local hardware store has a metric section if you want one or two (based on literally every local hardware store in my USA area) and if yours does not or you want to save a bit by bulk purchase, McMaster (or many other vendors) will have them shipped to you (you may need to buy 100 at once, but that's the cost-efficient way to do it anyway.)
    – Ecnerwal
    Commented Mar 23, 2015 at 20:21
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    As for the question of "correct usage" to put threads where there were no threads (on a precisely sized bit of stock, for a die) (in a precisely sized hole, for a tap) or to repair threads that exist, are the same size and pitch as the tap or die, but which have some damage that the tap or die can cut away to restore function (but not full strength, as part of the thread will be missing).
    – Ecnerwal
    Commented Mar 23, 2015 at 20:36

2 Answers 2

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If you're trying to completely change the treading on a nut or bolt with a tap and die, I don't think that's going to work very well. You may be able to get a new thread pitch, but it will be interleaved with the existing one, and all you'd be doing is weakening the thread material.

If you need to simply fix some mangled threads, then have at.

If you're looking to cut your own bolt threads, you will probably want to start with unthreaded rod. Although, as Cathode mentioned in the comments, if you have hardened steel rods, you're in for a lot of frustration and not much success.

I suppose you could chuck the bolt into a lathe and carefully (very carefully) slice the existing threads off to give you an unthreaded rod with with a nice bolt head, but then you'd have to grab a box of nuts of sufficiently small size that once you ground the threads out of the inside the resulting diameter would match up with your newly "skinified" bolt stock & you could rethread those.

All in all, I'd head to the local big-box and grab a box of what you need for your current project. You'll have some spares for the next project, and will, eventually have a few dozen of everything lying around that you can't find.

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    It should be mentioned that the grade of steel is going to determine success or failure. Trying to re-thread a grade 8 steel bolt will be an exercise in frustration.
    – William S.
    Commented Mar 23, 2015 at 16:59
  • Valid point, @cathode, answer updated to include that.
    – FreeMan
    Commented Mar 23, 2015 at 17:06
  • Plus Grade 8 bolts usually have roll formed threads to prevent stress risers. Cut threads can leave the thread root susceptible to fatigue fracture. Commented Mar 24, 2015 at 0:49
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I'm a gunsmith. The issue for me is on older guns that had some non-standard (by today) TPI count (e.g 1/4 - 24) Today it's usually 20 TPI for coarse or 28 for fine. I didn't want to have to weld a hex top to drill bar. So now I keep on hand 1/4 bolts with long unthreaded shanks and cut the threaded end off and make custom bolts (surprisingly it's not hard to get the dies you need). Sometimes the obvious solution stares you in the face.

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