This socket is constructed of high quality chrome vanadium steel (crv) with a chrome effect finish Chrome Vanadium Steel Mixed Security Socket Set includes 3/8" bits socket set: T10H, T15H, T20H, T25H, T30H, T40H and 178mm steel rail Large hard-stamped size markings allow for easy identification of socket size Durable and wipe clean for easy removal of oil and dirt Socket set has metric units of measurement