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

#12-40 is listed on eBay.

Thor

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

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

Apertures

MichaelG.

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.

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

can’t you screwcut it?

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 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

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