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Hugh · 04-28-2002, 11:24 PM

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.

04-28-2002, 11:24 PM	#1
Hugh RIP Join Date: Jun 2002 Location: Southeast Texas Swamp Posts: 2,460 Thanks: 2 Thanked 165 Times in 64 Posts	Barrel Threads revisited 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.