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