This type of interfacing is known as "fusible" interfacing. "Semi-enclosed fuses" are fuse wire carriers in which the fusible wire itself can be replaced. A thermal fuse is a cutoff which uses a one-time fusible link. Glass cartridge and plug fuses allow direct inspection of the fusible element. First, a core is made from a fusible alloy or low melting temperature polymer. The inner chimney is made of copper coated with a fusible metal. High voltage "expulsion fuses" surround the fusible link with gas-evolving substances, such as boric acid. Here the bars are extremely thin metal wires, and the switches are fusible links. Automatic fire sprinklers use a fusible element that activates at a predetermined temperature. It is a tough, malleable product, but not as fusible as pig iron. Cores are used for complex injection moldings in the fusible core injection molding process. Antimony has a crystalline appearance while being both brittle and fusible. New uses were found in fusible alloys, solders, and electronics. It may be protected from short circuits by means of fusible links. Not all locomotives are equipped with fusible plugs.