Radiator hose in-line fitting and 1/8 inch NPT port for thermostat switch. Fitting is measured by the outside diameter raised lip. Fixed turn-on electric cooling fan thermostat sensor grounding switch. Circuit closes at turn-on temperature and grounds your fan. Turn-off temperature is always 15 degrees less than turn-on. Mounts anywhere along the radiator or condenser hose line. Measures all liquids including water, coolant and oil. Universal for any car, truck, boat or other automotive project.