A fusible plug is a safety device designed to melt and release pressure when a system reaches a predetermined high temperature. They are commonly used in applications like boilers to prevent catastrophic failures due to overheating. Fusible Plugs are installed between the fireside and the waterside of either the plate, flue or tube of the boiler and below the water level. Those installed from the waterside are called waterside or inside type fusible plugs; those installed from the fireside are called fireside or outside fusible plugs. These single use plugs are filled with pure Tin that melt between 445°F & 450°F to serve as a warning device in the event water levels fall dangerously low.