You are buying a Set of (4) Standard 2" Heater or Pump Union Gasket. The gasket is 2 7/8" across on the outside the inside diameter is about 2 3/16" and the lip that fits into the union is 2 1/2" center to center and fits most unions but there a few exceptions so please measure. If you order this gasket and the ridge doesn't fit you union you can trim the ridge off and use it as a flat gasket. This part is used in hot tubs between a heater or pump union and the heater or Pump. We have plenty of these. Buy with caution I Do Not Accept returns! 

We offer these in sets as well of 2, 3, 6, 8 and 10 in our store!!  ,RMG-02-652G,gasket,gaskets,spa,hot tub, balboa,waterway, gecko, pinnacle, pump,heater, hydroquip,hydro-quip,2",3",15"