Hardened and tempered chrome-vanadium steel. Spring-loaded ball bearing. Fully polished and nickel chrome-plated for durable corrosion resistance. Supplied on storage rail. Contents: 1/4"F x 3/8"M, 3/8"F x 1/4"M, 3/8"F x 1/2"M, and 1/2"F x 3/8"M