Thermostat unit bolt. A threaded rod with a drive head (such as hex, 12 point, torx, etc.) on one end used to secure The Engine Coolant Thermostat to it's mounting point. Bolt used to fasten The Engine Intake Manifold. Engine Coolant Thermostat Housing Bolt. Engine Valve Cover Bolt. Coolant Housing. Flange. Intake Manifold. unit. Bracket. Control Assembly. Module. Valve Cover.