1/2 inch FNPT G style couplers are used in applications that require over 60 SCFM. There are two Milton G Style couplers, but both will function the same with G style plugs. Milton G style couplers are made of steel and are plated to resist rust. With a 1/2 inch basic airflow, these plugs offer up to 99 SCFM, making them the highest SCFM rated couplers. Maximum pressure of 300 PSI.