This item is a Black Replacement Diverter Cap for a 1" Waterfall or Neck Jet Control.. The inside thread measurement is about 1 5/8" and the center hole is about 3/4".. It uses (2) Small o-rings and one O-Ring Gasket that measures about 1 1/2" center to center..

 Other parts that fit this cap: Waterfall Control Valves & Related Parts