"...the change happened in 1963 around serial # 855,000 [change in style of barrel]. So if the barrel has a serial number on it then it is the old style with the pitched threads. The newer style barrels of the the interchanging type have no S/N on them. The old style threads are actually pitched just like a thread on a bolt. The newer style threads are straight V groove threads."
The barrel I have was from an M37 newer than S/N 850,000. Too bad, it's a 98% barrel.
Sorry
