Basic Size – This defines the air handling capacity of the coupler. The most popular size for automotive shop use is the ¼” Basic Size, which handles air volumes up to approximately 35 SCFM (Standard Cubic Feet per Minute). This size coupler readily connects and disconnects under normal air line pressure. The 3/8” Basic Size will handle air volumes up to about 60 SCFM. For air volumes above this amount, use the ½” Basic Size. These sizes are not intended to be connected or disconnected under normal line pressure. Do not confuse the Basic Size with the pipe thread size. The latter specifies only the size of the pipe fitting the coupler or plug connects to and has nothing to do with air volume.
Style – Ten different coupler/plug styles are in current automotive and industrial usage. They were originally developed by different coupler manufacturers. There is no advantage of one over the other, although the Industrial Interchange types (Styles M, H & G) are the most popular. Normally, the various styles are not interchangeable. But all couplers and plugs bearing the same letter (e.g., M-style) will work together. Notice there are two G-styles with different plug designs; these are interchangeable.