Krag stacking swivel screw size/thread

[Der Jagar]

Recently bought a Krag rifle (1901 DOB) that lacked a stacking swivel. Bought one from a fellow 'MILSURPS' member with a screw. Screw I received fine, outer edge of upper band where it attaches has some thread issues that won't allow screw to turn in all the way. Anyone know what size and thread pitch is. Appears to be a #10 screw (?) with a thread pitch somewhere between 32 and 24 tpi. None of the screw checkers I have seem to have right pitch to measure. Need to clean up threads on upper band.

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[rcathey]

Do you think the threads would clean up with a needle file? I have a few pretty fine ones that may work for you. Wouldn't mind at all sending you a few, on me.

[Der Jagar]

rcathey- Thanks for the offer. I have several good sets/grades of needle files, but the threads that need some TLC are just inside of the threaded hole on the outside of the upper band. I can screw the screw just within about 3-4 threads from being seated. I don't want to force it and strip what is there. If I had the right tap it would be a breeze. I have a number of gun screw size taps and dies, but the size I need isn't in my collection of course. Appears to be a size 10 screw with threads finer than 24 tpi and courser than 32. Don't have any taps that size. Do have a gunsmith not to far away who is a whiz on military and older firearms I can take to him if push comes to shove. I did read somewhere that the author made mention that the Krag rifles used some unusual thread pitches, don't know how true, but possible I guess.

[Salt Flat]

DJ, I believe they are 26 TPI. Do a google search on the Krag Collectors Forum. They have some info on this. It might be real hard to find a tap that size. Salt Flat

[Der Jagar]

Looked through the Krag Collectors Forum and found several threads and posts about thread sizes on Krags and the stacking swivel screw. One post advised most Krag screws are either 26, 28, or 30 tpi depending on the location. This could possibly confirm what I read somewhere else that the Krag is a firearm with 'different' thread pitches. Anyway the stacking swivel screw is supposed to be a 0.187 shaft diameter which according to a chart I viewed would be a #10 screw (comparable to what I checked), with a thread of 26 tpi. My thread pitch tool showed that 24 tpi was to course and the next leaf was 27 tpi which was to fine. A 26 tpi probably would be right on. No such tap or die in my collection. Will have to consult with my gunsmith source. Curious. Thanks for the lead Salt Flat.

[rcathey]

What about getting a spare screw, cutting a groove down it lengthwise, and running that through a few times? For minor thread boogers, this’ll usually work.

[Der Jagar]

What about getting a spare screw, cutting a groove down it lengthwise, and running that through a few times? For minor thread boogers, this’ll usually work.

I'll keep it in mind, good suggestion-never have gone that route, I've used a harder steel screw to clean up threads in a softer steel though(sort of the same principle as a tap). The gunsmith I mentioned earlier is a old time 'smith' who loves 'older' guns. If he can't find a part, he can make one, never have heard of anything that stumps him. I'm wondering if these 'oddball' thread sizes are just unique to the Krag or other guns of that era. Have never heard otherwise. I have other military rifles form the WW1/2, Korea, but have never had to seek or repair any screws/threads for them, just always used what they came with. Wonder what the Trapdoor used? I have dealt with percussion revolvers of the 1800's, but they're of the reproduction lot. Just bought a 03 Springfield not long ago, the next in line so to speak of the US Military issue, I have no idea if the military continued with these thread pitches with them or not. From what I've read some of the same parts or style used on the Krag were inherited by the 03. Did read a short bit some time back when the article mentioned the odd thread sizes of the Krag that they inherited some European traits in that respect being they were designed by Norwegian designers. Wouldn't think the US at the Springfield Armory would have continued the use over using whatever was more common in the US. "Above my pay grade"! Be something to read up on. I've read a lot on military firearms, but thread pitch is something I've rarely seen, always give screw diameter, length, head size, how much of the end was threaded, but rarely thread pitch-at least in the sources I've read. The journey continues.

[no4mk1t]

The thread standard in use at the time the Krag was manufactured was United States Standard (USS).
This is an obsolete standard that is quite different from SAE and metric threads in use today.
I would contact S&S in NY. They are reproducing screws in this thread pitch, or have originals for sale.
United States Standard thread - Wikipedia

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[rcathey]

A reproduction screw would be a good choice for the idea I shared above.

[butlersrangers]

I have been guilty of posting my observations, measurements, and suspicions about the origin of U.S. Arsenal screws and threads, on the KCA Forum.

(My WAG is that the threads may have been influenced by the French Military Arms we first copied at our Manufactories. I would be delighted if a knowledgeable machinist/engineer/researcher could throw more light on the subject).

In regard to the Krag 'Stacking-Swivel Screw', the thread size is approximately .187" X 26 TPI.

The same thread size is also used for the Barrel-Band Screw and the magazine side-plate screw. This thread size is also used on 1903 Springfield Swivel-Screws.

IMHO - A number of things happen to interfere with a good fit and caused damage to threads.
1. Wrong screw - wrong length. (A lot of Springfield screws were similar and had the same thread, but, the various screws were specific to their function and had differences. Over the years, the wrong screws sometimes got used).

2. Swivel-Screw tips were 'mushroomed', which deformed threads. (This was intentionally done to prevent loosening and loss. When such screws are removed, the threads are further deformed).

FWIW - On a number of Krag rifles, I have seen the 'Stacking' and 'Barrel-Band' swivel screws mixed-up.

Attached is a photo that may help identify and display their differences.