M1917 Screw Thread

[gunboat57]

I have a Remington made M1917 in very good condition. I am designing a compact rear sight for it which can be easily adjusted for windage and elevation. I won't alter the rifle other than removing the military sight and attaching mine.
One point for attachment is the hole for the screw that retains the rear sight spring. On page 88 of my copy of Charles Stratton's book, he says the screw is .14" diameter and 37 threads per inch. The M1917 and P-14 use the same screw.

Can someone explain where this weird screw thread came from? Could this be a mis-identified 6-40 thread?

I was able to twist a 6-40 bottoming tap into the hole all the way to the bottom using fingers only with no resistance.

[elk hunter]

As I understand it the P-14 made in the US for Britain during WW-1 was built to British specifications including screw diameter, pitch and thread form. The US M-17 was built using the same machinery and specifications except caliber. IIRC it was about WW-1 that Britain and the US started standardizing screw diameter, pitch and thread form so there would be interchangeability. The British used the Whitworth standard for a very long time. Have you ever worked on a British motorcycle from the 50's or 60's? If so you were introduced to the Whitworth standard/system.

[gunboat57]

Thanks for the reply. I've been looking online for any reference to a 37 TPI screw with a major diameter of about .14 inch. Do you know of any? Was that a British proprietary military screw specification?

[Der Gebirgsjager]

Going by your description of the 6-48 tap easily screwing into the hole it seems that a 6-48 screw should work. But, will only one hole be sufficient to hold the sight firmly? You may find yourself drilling a second hole, and if that turns out to be the case 6-48 is a logical choice.

DG

[elk hunter]

Thanks for the reply. I've been looking online for any reference to a 37 TPI screw with a major diameter of about .14 inch. Do you know of any? Was that a British proprietary military screw specification?

I checked (Machinery's Handbook) and didn't find any 37 pitch screw threads listed in British Whitworth Standard, British Standard Fine, Unified threads or any American type. The 37 pitch may have been some sort of standard before the Unified series was adopted. Sorry I can't be of further help.

[gunboat57]

Thanks for checking. The closest thing I found was a British Association size 4 thread which has a .1417" major diameter and a pitch of 38.48 threads per inch. That is very close to a 6-40 thread. Close enough for me to run a 6-40 tap into the hole for at least a quarter inch without feeling any resistance. Another one of life's mysteries I guess.

By the way, I like your signature. I have hunted groundhogs with rifles ranging from 577 Snider and 577-450 down to this year's favorite: 22 Hornet.

[challenger_i]

577... Bet THAT leaves a mark! :)

[gunboat57]

Ha! It would've left a mark if I had ever connected. Turns out me and my Snider-Enfield were more bark than bite when hunting groundhogs! It was fun though.

Elk hunter, I measured the mystery screw while backing it out 1 turn at a time. It advanced .025" per turn exactly. Or 40 TPI. So much for the 37 TPI myth. I'll be getting some 6-40 screws today to try for fit.

Only other remote possibility would be an M3.5 X .6 screw. That works out to 42.3 TPI with a major diameter of .138 inch just like the 6-40.

I'll report my conclusions, just for reference, when I finally give up.[smilie=b:

[JHeath]

I work at a fastener supply company.

Old guns and sewing machines sometimes have oddball thread pitches. Manufacturers made their own screws, so designed whatever they wanted and turned them. I don't know about the M1917 thread specifically.

Sometimes you can match an old one with a metric thread, like the #3-56 nut I needed for a Lyman sight matched 2.5mm pretty well. In a deep tapped hole it might not have worked, but for the depth of a nut it was a perfect fit.

Or an 11mm-1.25 (tough to find) is almost exactly the same as a 7/16"-20.

Old Schwinn bicycles had proprietary threads to force owners to buy only Schwinn parts.

I wouldn't count on an M1917 having threads matching the limited modern selection.

[gunboat57]

Yeah, I should be used to encountering obsolete and proprietary screw threads by now. But if you work on old guns or sewing machines it goes with the territory.

Got my 6-40 machine screws today. They thread deep and solid into my M1917 receiver. So I say "good enough" and "case closed" until further evidence becomes available!

[Tedly]

Shortest distance between two points , take your sample (or get one) and go to a local toolmakers shop (tool& die) , ask somebody there to check it . Machine shop can tell you , zero guess ,
I'd look at it and tell you if you were in Detroit