M6X25X18. Bolt. AT:6 MT:4. 6X25X18. Engine Coolant Thermostat. Engine Water Pump. MT.20D20V:4 25D:2. Radiator Mount. 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 its Mounting Point.