Eutectic alloy is filled in the stainless plug. Fusible fittings function by the yielding or melting of the fuse alloy. Fusible fittings are thermally operated but not reusable pressure relief devices. Fusible fittings do not protect against overpressure from improper charging practices. Maximum operating pressure: Tested to 500 psi (3.4 MPa) Two types of fusible fittings: Pipe plug and tube adapters with 316 stainless steel body.