Choose between a 1/4" Male or 3/8" Male Stainless Steel Quick Connect plug.
As a rule of thumb, MTM Hydro 3/8" fittings are normally found between the pump and the spray gun where 3/8" hose is commonly used.. When purchasing plugs and couplers the Male model has exposed threads while the Female version has threads on the interior of the fitting.
This is the male model