3/8 in 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 in basic flow size, these Couplers offer up to 99 scfm, making them the highest scfm rated Couplers. maximum pressure of 300 psi.