??? Original Krag Rear Sight Screws Threads ???

[LHSM]

Hello All

What Are Threads in Original Krag Rear Sight Screws?

Neither 8-40 8-36 nor 8-32 seem to fit properly in two original
barrels that I have.

Thank you.

LHSM

[madsenshooter]

Uh, oh, here we go. They are, quite by accident, because we copied the French so closely, an M4x1.0mm thread. The French had a lot of influence in our early armories. Now, the bad news. The current standard pitch for an M4 screw is .7mm. I have upon occasion found M4x1.0mm pitched screws in old Japanese made scope rings, the type that went on grooved receivers, so they used to make them. Good luck finding any today! It would probably be easier, and cheaper, to d&t to something larger, and standard.

[LHSM]

To Madsenshooter

Thank you very much for answer. !!! I thought possibly it might
be one of the M4s there are four pitches in that dia listed in
the msc.com machine shop catalog. But the longest pitch they
show is M4 x .8

I want to use original screws so I can use the M1901 rear sight with
aperture - the front screw there has that long head to serve as
a pivot for the windage, as you may know.

What I want to do is D & T one of the criterion barrels that CMP
was selling in August, to take the original screws. Those Criterion are
threaded 6 x 32 !!! , no fooling. I called Criterion and they
put themselves in writing.

Do you know anyone who is shooting a Krag with one of those
barrels yet? If so do you know what they did about
mounting a sight on the barrel ??

Thank you for prompt answer

LHSM

[Parashooter]

http://telecom.hartford.edu/images/kragscrew.jpg

Whatever the original screw thread is - M4x1.0 ain't it. Here's a picture of an original Krag sight screw next to a 28 TPI pitch gauge. As you can see, the pitch is a hair tighter than 28 per inch, more like 29 - a real oddball. In any case, it's not even real close to 1.0mm (25.4 TPI).

[madsenshooter]

Yes, I know some people who have used the Criterion barrels. 6x32 socket head cap screws is the way to go. You can turn down the head on one of them so that it becomes the pivot for your sight. That's what the guys at the CMP who contracted for the barrels told me. You can find the screws at your local hardware and save yourself a lot of trouble. Local hardware doesn't have them, Fastenal does. They were commonly used as scope ring screws too.

Shooter, someone must've stretched that one. I can put a pair of reading glasses on top of my bifocals, measure from the top of one thread to the next with my newfangled digital calipers, and I get exactly 1.0mm. You sure that isn't trapdoor screw, I don't have any with threads squared like that. They're a nice sharp V. I got half a dozen of them sitting here in front of me, oh wait there's one with squared threads, but it measures the same 1.0mm. Oh heck, t'ain't worth arguing over, use the 6x32s LHSM, they're certified CMP legal, and cheap!

[LHSM]

Madsenshooter
Thank you very much for info about criterion barrels.
LHSM

[madsenshooter]

OK, but in return you have to promise to be at the Vintage Match at Camp Perry next year, we want to make the Krag's presence known, and I can't shoot offhand worth squat. We gotta get Bob S. there too.

[Dick Hosmer]

AFAIK, the standard thread used at SA - a CLOSE copy of the French 1mm (25.4tpi) pitch - is 26tpi. That shows up in MANY applications - only the diameter was changed to suit the particular need. Perhaps the screw shown against the thread guage is not REALLY a correct screw?

[Parashooter]

Perhaps the screw shown against the thread guage is not REALLY a correct screw?

Operating on this possibility, I checked the other sight screw from my 1898 plus two from an 1884 Trapdoor (Buffington sight) and all were a good fit in the holes in both barrels plus a spare 1898 barrel (original). I'm confident pitch is the same on all four screws and I have no good reason to suspect any are not original. Again, a close look with the pitch gauges shows they are all a hair tighter than 28 TPI (which is virtually identical to 0.9mm) but definitely not really close to either 1.0mm or 26 TPI.

http://i54.tinypic.com/dbk215.jpg

http://i54.tinypic.com/2usgxlu.jpg

http://i53.tinypic.com/5fq9vt.jpg

If any of you would like to help nail this down but don't have pitch gauges handy, the best way to get an accurate estimate is to measure the distance (in inches) between several crowns, divide to get the distance between individual crowns then divide 1 by that number to get TPI. Trying to measure the distance between adjacent crowns on these little screws is just too difficult with a common caliper, even with magnification.

Madsenshooter - These are not actually "square" threads. What we're seeing in the macro photos is the truncated crown typical of standard threads. It's just that we don't normally look at them this closely. As for being "stretched," think about whether stretching could make the pitch tighter.

http://upload.wikimedia.org/wikipedia/commons/thumb/4/4b/ISO_and_UTS_Thread_Dimensions.svg/800px-ISO_and_UTS_Thread_Dimensions.svg.png

[JimmyK]

Years ago I bought an old Swedish tap and die set with a number of (now unusual) size taps and dies. US Krag rear sight screws are 30 tpi and mike .159" (4 mm) in diameter. US Krag triggerguard screws are 25 tpi x 1/4". These measurements were derived by actually checking an original US Krag screw against one half of the split dies.

A brass 8x32 screw can be pressed into service as a sight screw in original tapped barrels. The brass threads will deform enough over the short engagement distance that they do not seem to damage anything. Personally, I would rather have a new barrel tapped for screws that are readily available--6x32 (a standard regular duty scope screw size), 8x32 (brass hardware store screws) or 8x40 (a standard heavy duty scope screw size).

[JimmyK]

Just found this source for 5/32" x 30 tpi taps--Victor Machinery Exchange. They are listed as 8 x 30 tpi taps: http://www.victornet.com/subdepartments/Special-Pitch-Taps-up-to-1/2-inch/1260.html

[Dick Hosmer]

While I respect your input, I seriously doubt the accuracy of your statements of 25 and 30 tpi. Was the "old Swedish tap and die set" graduated in English or metric units?

I also (always) respect Parashooter's highly detailed presentations, but have never seen anything in contemporary literature to support the use of such odd sizes. The 26 tpi info has been widely published for years, and, at least on the larger sizes, has not been questioned.

FWIW, 26 tpi was once fairly common in the British bicycle industry, so that is another possible source of tools.

Has the supply of original Krag screws completely dried up, or is it just that the prices have risen so high as to cause a panic?

[5MadFarmers]

To me it looks like you're all screwed.

[Parashooter]

Here's one more attempt at getting a handle on the actual pitch of these little buggers. Doesn't prove anything for sure, but I'm now satisfied 30 t.p.i. is what this apparently original screw has -

http://i51.tinypic.com/2uf6hvr.jpg

If I were enlarging the holes in one of the new CMP barrels to accept this screw, I'd be ordering one of those #8x30 taps from Victor Machinery Exchange. Kudos to JimmyK for finding a source.

[JimmyK]

The Swedish tap and die set is fractional and was probably made for export. It is a very high quality set that I'm guessing was made in about 1920-1940. Some of the taps and dies contained in the set are standard UNF/UNC sizes but when I noticed all the unusual sizes and the two piece die design it became a must buy. Oddly enough, my metric set of taps and dies was made in the USA. Go figure!

I remain quite sure that the rear sight screws are threaded 5/32" x 30 tpi (or 8 x 30--USA not metric) and the Krag/Springfield 1903 triggerguard screws are 1/4" x 25 tpi.

I rechecked a triggerguard screw against my 1/4 x 26 tpi die and it is a no go. The threaded portion rocks in the die slightly so it's close but not correct. Incidentally, Whitworth (BSC) taps and dies are available in 1/4" x 26 tpi but the 55 degree thread angle is a slight mismatch for most other threaded product standards which use a 60 degree thread angle--USA threads included. It is not suprising that BSA products being English made, used a common British standard for their threaded components. Even today, many different threading standards continue to be used despite efforts to create one worldwide system.

The original inquiry was for the tap size needed for drilling and tapping a barrel for original size sight screws. So far as I know, reproduction rear sight screws are available from S&S Firearms and T/G screws from a variety of sources. The T/G screws are listed usually as 1903 Springfield T/G screws as this part was just carried-over from Krag production.

[5MadFarmers]

It's never where you look for it is it?

I am not a machinist.
I don't play one on TV.
I didn't sleep in a Holiday Inn Express last night.

A standard Frankford Arsenal tap and die set (1902) contained the following:
0.062 x 60
.08 x 60
.09 x 43
.1 x 43
.125 x 43
.156 x 30
.187 x 26

They call them "United States Form." They had taps/dies for "U.S.F. Special" and "W.&S. Standard." Whatever that is.

FWIW.