Spark plugs are unique. You need a strong tool to release stubborn stuck plugs yet a soft touch so you don’t do any damage. The Powerbuilt 3/8-Inch Drive 21 MM Spark Plug Socket is strong as well as protective of the spark plugs. The premium Chrome Vanadium steel socket has a mirror polished chrome finish for durability yet has an innovative rubber insert to protect the spark plugs and center hole punched for added work depth. The sleek chrome finish is enhanced with an easy-to-read size marking that is forged into the metal socket. Precision chamfered 6-point hex faces easily guide the sockets onto fasteners and allow for a more solid grip on the flat surfaces to prevent damage or rounding. An external hex bolster allows for additional turning options. Powerbuilt sockets exceed ANSI standards.