Based on a number of serious incidents with valve threads not matching cylinder threads the CGA has developed a code for marking standard cylinder valve threads currently in the United States and Canada. This technical bulletin explains why a cylinder thread code is needed and also explains why both the cylinder and valve need to be so marked

CGA TB-16
Original price was: $161.00.$80.00Current price is: $80.00.
Recommended Coding System for Threaded Cylinder Outlets and Threaded Valve Inlets
Compressed Gas Association , 09/01/2010