Common Action guard-screws - thread & sizes

[butlersrangers]

I ran across this today while looking for something else, the work of the-late Frank de Haas.

It is handy to have on one page!

[FredC]

That is a handy list, I did not see a metric pitch in the bunch. With an English or American lathe with an 8 thread per inch lead screw, 24 or 32 threads per inch are the easiest to thread. You do not need to look at the threading dial, any position will line up.

Funny machinist story, I was making Mauser screws for Mr. Kleinguenther and was convinced the Mauser would have metric threads. The closest metric match I could come up was 1.15mm. I had to use an unusual mix of gears to get that pitch. Years later I found out the real TPI for Mauser is 22. That one was on my lathe chart and would have been easy.

[butlersrangers]

The Italian Carcano screws are a surprise (1/4 X 25). It would be interesting to try the fit with Krag and Springfield receivers?

[FredC]

If the Italians used the same rounded crests and root on the thread form they could very well be interchangeable. The other possible problem could be the flank angle, the only major one that I know of that used the 55-degree flank angle is the English Whitworth system. If they were ahead of the game and used the small flats on the crests and roots that we use in the unified and metric systems then the crests of their screws will interfere on the roots of Krag or Springfield receivers.

If you find a Carcano screw it would be easy enough to check.

There are a couple of 26 TPI on the chart and I have to wonder if they are not rounded up 25.4mm.

[butlersrangers]

It is interesting that the British Lee-Enfield used 1/4" X 26 thread and Pattern 1914 - U.S. model 1917 used 1/4" X 30.

[FredC]

There probably is a story behind each one of the choices. Late Remington is pretty obvious, they abandoned the legacy screws and adopted UNF threads. I do not have my Machinery's Handbook at the house, but I think the late Winchester is UNEF (Unified Extra Fine). Others stuck with legacy even though the countries where they were built went metric. Engineers, designers weighed whether they wanted the strength in the receiver threads or the screws in deciding between fine and course threads. Egos were probably in the mix.
A couple of the numbers make my suspicious side think that they are really metric.