This adapter is a push-on style, and secures to most modern USA, European, Japanese, etc. fuel injection systems and are used to convert an OEM SAE Quick Connect connection.

To determine the required size, simply measure the outside diameter of the male fitting as shown below.
0.3125 = 5/16″
0.375 = 3/8″
0.50 = 1/2″

IMPORTANT: Always lubricate the mating O-rings with a light amount of oil prior to installing.