This tool is designed to make the installation of a 5/8" x 3/8" compression angle valve easy. Just open the end of the tool, place it around the 5/8" nut & tighten. Flip the tool around & tighten the 3/8" supply line nut in the same way. The ratcheting mechanism allows you to never have to take the wrench off of the valve until it is tight. Works great on any 3/8" or 5/8" compression nut. This tool can be used in conjuction with the 4525 Angle-On Wrench.