American Spa Parts 2" Heater Union Split Nut Kit with Gasket O.D. 3 1/4" 3 1/4" Outside Diameter 2 1/4" Inside Diameter Gasket Rib Size 2 1/2" Fits Most 15" Spa Heater Unions Look for our YouTube video about this union called "Hot Tub Spa Part 2" Heater Split Nut Information How To"