Anvil Brewing Equipment’s #7-4 Hole Stopper is made of natural rubber and has four holes that accommodate the Anvil Cooling Coil, the Anvil Thermowell, and an airlock. It has one 9.5 mm hole, two 5.7 mm holes, and an 8.5 mm hole. It works great as a replacement in the Anvil Cooling System if yours is missing or damaged.