Radiator Pressure Relief Valves.

This valve is used with Spirit's aluminum T-bucket radiator. It threads into a 1/4" NPT hole in the top radiator tank and it limits the pressure in the radiator to 15 psi.

The aluminum T-bucket radiator does not use a conventional "pressure" radiator cap, rather it uses the decorative "T" caps to seal the neck at the top of the radiator.