Pair of 1.5 Inch Heater Split Nuts for Flow-thru heater housing unions. They are made to replace heater flange nuts. The overall diameter is 2-3/4" and the flange side opening is 1-7/8". They have a large flange for stainless steel housings and are for heaters only. Some of the major brands they will fit; Allied Innovations, Balboa, Cal Spas, Gecko, Gulf Coast, Hydro-Quip heater assemblies, along with many others with metal 1.5" heater assemblies.
Note: The 1.5" is not the actual measurement but a representation of the inner diameter of the plumbing that is used.
Manufacturer's 1 year limited warranty free of defects