A method for forming a resin molding on a coil of a transformer is disclosed. In the field of magnesium metallurgy, no secondary alloys have existed so far such as they exist in the case of other metals such as aluminium, for example. As a safety factor in the event of leakage in the casing, a check valve is inserted in an effluent blood duct from the casing to the aerated effluent blood. The present tool allows the wires to be held to the shaft of the tool after they have been bent inwardly from the head, thus locking them in place about the shaft.