This Kit is a Combination of the Two Standard Size 2" Heater or Pump Union Gasket (1) with a 2 1/2" Lip Center to Center and (1) with a 2 5/8" Lip Center To Center. The purpose of this Combo Kit is if you don't know which size you have you get both.. Use One and throw the other away.. Gasket #1: 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. Gasket #2: The gasket is 2 7/8" across on the outside the inside diameter is about 2" and the lip that fits into the union is 2 5/8" center to center and fits some unions but most unions are 2 1/2" center to center..