In some cases, it is difficult to visually determine if the threads on a valve are mismatched to the threads in a cylinder after a cylinder valve has been installed into a cylinder. Identification systems and markings on valves and cylinders are used outside the United States that permit cylinder fillers and users to see if the cylinder valve and the cylinder have the same threads. The Compressed Gas Association (CGA) recommends that a coded marking system be used in the United States and Canada to ensure that valve threads and cylinder neck threads can be identified and matched when the valve and cylinder are assembled. This bulletin outlines the coded marking system to be used to identify and mark valve threads and cylinder neck threads.