The FT151 thermo-optic sensor contains the FT150 probe and a 2" NPT housing. Our probe holder is cast aluminum with a 2" NPT mounting thread, heavy duty stainless steel hardware, and Viton® probe seal. Install in a 2" NPT tapped hole or 2 3/8" hole using the gasket and locking nut provided. All screws and rings are heavy duty stainless steel for easy assembly and long life. Compatible with Scully Intellicheck monitors.