Aluminized Plug Wire Sheaths 4 Pk. - Made from the same material as Heat sheath the plug wire sheath was designed as an inexpensive way to protect ignition wires and plug boots that run close to exhaust manifolds and headers. The Aluminized Plug Sheaths can also be used on lines, wires and hoses. Each Sheath measures 3/4in. diameter by 6in. long.