This replacement split nut has a larger inside diameter on the collar than those usually used on spa heaters but has the same thread size. It is designed to go over the larger diameter plastic inserts found on pump unions.

This union has the "standard" 2 inch union thread found on many brands of industry equipment - Waterway, Aqua-flo, Sta-Rite, Acura, Vico and many others use this thread on some or all of their 2" pumps. This is also known to fit the Aqua-Rite and Naturesoft Chlorine T-cells.

The inside thread dimension on this split nut is approximately 3".