Barrel Threads revisited

[Hugh]

A barrel thread is specified by its "pitch", expressed as the number of threads per unit of linear measure, its "form", or thread profile (square, V-type, etc), the "thread" angle formed by the sides of the thread, and the diameter of the threaded tenon. Over the years gunmakers have combined these parameters in a seemingly endless variety of barrel thread patterns.


The Whitworth thread system, the British standard from the 1860's to after WWII, was a 55deg V-form thread with rounded thread crests & roots. The American National screw-thread system, standardized in 1933, used a 60deg thread angle with small flats at the crests & roots.


Though the Whitworth and American National were both inch-based measuring systems (that is, the pitch was expressed in threads per inch), their different thread angles led to interchangeability problems. In 1949 great Britain, Canada and the US adopted a Unified Thread system that retained the 60deg angle of the American system but permitted both flat and rounded crests. Many older foreign actions like the Luger employ a V-type 55deg Whitworth-type barrel thread. Current American, British, and Canadian actions generally use a Unified barrel thread. Metric barrel threads are also found on a number of foreign actions. Now uncommon, square threads were once popular, and can be found on the '03 Springfield, M1917 Enfield, M1 garand, and others.

[John Sabato]

I know I had that information filed away in my head somewhere, but my filing system is beginning to need some work...


regards,


John

[Hugh]

Rick, if they are of recent manuf, I pretty sure they are 60 deg.

[Hugh]

Rick,


I just checked the Luger barrel tap and die set that I have and it is marked: N18x1.27, which I assume would mean a National thread, which would be 60 deg.