This Part is a Set of (2) Standard 2" Heater or Pump Union Gasket with a lip that is 2 1/2" Center to Center. 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 offer these in sets as well of 3, 4, 6, 8 and 10 in our store!!