GearWrench 3789 Universal Adapter 3.75” x 7.75” Diameter GearWrench 3789 Universal Adapter 3.75” x 7.75” Diameter for Brake Bleeders 2901D and 3795D requires brake bleeder adaptor 37951, pressurize brake systems on many applications across many makes, use with rectangular reservoirs under 3.75” x 7.75” common on trucks and full sized vehicles.