3/8 '' FNPT G style couplers are in applications that require over 60 SCFM. There two Milton G style couplers, but both will function the aforementioned with G style plugs. Milton G style couplers are of steel and are plated to resist rust. With a 1/2 '' base flow size, these couplers up to 99 SCFM, making them the highest SCFM rated couplers. Maximum of 300 PSI.