Comparison : Item # 21F4M, Straight Coupling Medium Pressure Fittings
Item # 21UF4M, Union Coupling Medium Pressure Fittings
Item # 21F6M, Straight Coupling Medium Pressure Fittings
Item # 21UF6M, Union Coupling Medium Pressure Fittings
Item # 21F9M, Straight Coupling Medium Pressure Fittings