Conduit and fittings form systems to route and protect wire and cable. Conduit encases conductors to prevent environmental and impact damage and prevents people from touching wire. Metallic conduit is crush-resistant and intended for heavy-duty applications. PVC conduit is lightweight and suitable for outdoor use. PVC-coated metal conduit is ideal for routing wire and cable in highly corrosive environments. Flexible conduit is used where wire needs to make tight bends or withstand vibration. Liquid-tight conduit resists moisture. Sealants, fiber fillers, and anti-oxidant compounds seal conduit and fitting connections, insulate conductors inside conduit, or remove oxidation from fittings. Each type also has specific fittings that join pieces of conduit together or join them to enclosures and devices. The fittings are not interchangeable among conduit types.