Set of (2) 2 1/2" Spa Hot Tub Pump Union Therm T Gasket 3 1/4" O.D. 2 3/4" I.D. 3 1/4" Outside Diameter 2 3/4" Inside Diameter Fits 3" Heater Tube Union Fits Some Spa Heater Unions Lip 3 1/8" Center to Center