These adapter fittings are available in a variety of configurations. They push-on and secure to most modern USA, European, Japanese, etc. fuel injection systems and are used to convert an OEM SAE Quick Connect connection.  Scroll down for a photo of each part number. MEASUREMENT To determine the required size, simply measure the outside diameter of the male fitting as shown below. 0.3125 = 5/16"0.3750 = 3/8"0.5000 = 1/2"0.6250 = 5/8" IMPORTANT: Always lubricate the mating O-rings with a light amount of oil prior to installing.