7/32-40 UNS die needed

Good afternoon all.

My current project requires a 7/32-40 UNS die. All I can seem to find with a Google Search is ME dies, but as I understand the thread angle of these is 55, and the UNS is 60.

So the question is, does anyone know a UK based online resoure for UNS dies?

Cheers,

Bob

Tracy Tools list 7/32" UNS as 24, 28, 32 & 36 TPI NOT 40TPI??

Robert Butler

Edited By Robert Butler on 05/09/2022 13:20:47

Edited By Robert Butler on 05/09/2022 13:22:36

Might be worth trying #12-40 rather than 7/32-40 as below 1/4" they use a number system.

My usual chart does list it under UNS but as you say not many about in teh UK

#12-40 is listed on eBay.

Thor

Thanks gents.

I looked at Tracy Tools but as said they don't list the 7/32-40.

A bit wary of the ebay offering as it appears to originate from China.

Will look into the 12-40, might have to end up getting one from the States.

There is no mention of 7/32"-40 UNS in any of my professional engineering books. I would agree with JB that 12-40 is the closest listed thread.

From a practical point of view it should be easy enough to screwcut. Alternatively the difference in width at the base of the flank between the hypothetical 7/32"-40UNS and 7/32"-40ME is less than a thou. So unless the application requires precision fits a 7/32"-40ME die will be fine.

Andrew

Interesting, thanks Andrew.

I'm wanting to make some apertures to fit into a Skinner rifle sight. I was originally going to get the ME die, but some online reading suggested the pitch difference in the threads wouldn't work at all.

In terms of the application, it's going in a 7/32-40/12-40 hole on a sight fitted to a .44 magnum rifle. Although there will be significant recoil, if I can get the aperture tightened into the sight it should all be good.

This would seem to confirm that 12-40 is Skinner’s thread: **LINK**

http://skinnersights.com/apertures_8.html

MichaelG.

Yes, Skinner states 12-40, however online reading suggested the 7/32-40 was more prevalent and would work.

I notice that 12 size unified is only 0.00275" smaller than 7/32", so if you can get a split die, the size could be matched pretty well.

Agreed, I think (from what I read online) that's why the 7/32-40 was recommended. Also because other sight makers (Willaims, Lymans, etc) seem to favour this over the 12-40, so I could always make apertures for other club members if required.

However I still have the issue of where to get a 7/32-40 UNS die from without importing from the States. To answer my own question, I don't think I will be able to, unless I risk it with the ME equivalent.

Zeus Charts list 12-24 ANC as 0.216", 12--28 ANF as 0.216" diameter

Since 7/32 is 0.218", If yo use a 12-40 UNS die, you are likely to produce what you want.

Being 0.002" underisze will probably be the truncation applied to Unified threads, so you should have no problem.

Tracy Tools list 7/32 x 36 UNS and say "Many more sizes not listed" so they can probably supply what you want.

I suspect that 7/32 is being quoted as the nearest fractional size to the size 12 Unified threads, so I would turn the blank to 0.216" before using the Dies, since that is the specified OD.

Howard

Good suggestion, I will call Tracy tomorrow.

can’t you screwcut it?

Possibly. I'm not sure if my lathe (WM180) can cut that thread, and I've never cut a thread that small before. However, I may potentially be making a few apertures so it seems to make sense to go the die route. Work smart and not hard.

I've never heard of a 7/32-40 UNS on this side of the pond either..... #12-40 UNS, sure.

My guess is that someone, somewhere has "rounded off" the #12 for his own purposes .... possibly to emphasise that it can be die-cut on 7/32 rod. Although, given that UNS is reserved for "Special" threads, I guess people can make what they want, both in dia and tpi as long as they stick to the UN thread form. Getting commercially available dies in that case might be problematic though.

Just an aside:

I may be wrong [it’s happened before!] but … looking at the modus operandi for these sights, I would be very surprised if the manufacturers cut their threads ‘from scratch’ with a die: It would be preferable to screw-cut it in the lathe [and only use a die for final sizing, if necessary].

MichaelG.

.

Edited By Michael Gilligan on 06/09/2022 04:44:09

Just had a look for a decent picture of the Skinner item

The one at bottom-left of this page: **LINK** is the best I could find

https://gunblast.com/SkinnerSights.htm

[click the picture for a better size]

It certainly appears that Andy* makes a good job of the threads [which look much better finished than the knurling]

The next question must be : Being Unified threads … which class of fit is used ?

MichaelG.

[*] **LINK** http://skinnersights.com/the_shop_9.html

Ref. __ **LINK** https://www.fastenal.com/content/feds/pdf/Article%20-%20Screw%20Threads%20Design.pdf

Edited By Michael Gilligan on 06/09/2022 08:10:53

If your lathe is metric only cut a 1 mm pitch it will fit especially the number of threads you need, it will be finished before you’ve filled in an online order .

How does that work Bernard, 40tpi is 0.635mm pitch