The gasket is 2 7/8" across on the outside the inside diameter is about 2 3/16".. The lip that fits into the union is 2 1/2" center to center... NOTE: This will not fit a Saluspa By Coleman so do not order for that tub.. Note: DO NOT Order this if you are not willing to look at the pictures and Measurements.. Everytime you order this 5.89 parts and ship it back we pay almost 7.00 for your mistake.. QUIT Ordering the wrong thing!!!!!! 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!!