Master mechanic, 5/16" x 4-1/2", high speed steel, black oxide drill bit, 135 split point, jobber length, straight shank, 135 point angle with 4 cutting edges which eliminate walking & provide fast penetration, black oxide tempering treatment reduces frictional resistance & improves chip flow, recommended for wood, plastic, wallboard, plywood & soft metals, aluminum, brass & bronze, for occasional use in stainless steel & other hard metals.