metal; plastic [VERSATILE]: This fastener bit set features 10 metric bits with the 3 largest sizes being tamperproof. Triple-square spline sockets are ideal for use with tamperproof lug nuts, cylinder head bolts, and other engine bolts. [DESIGN]: This kit can convert standard square drives to triple square bits and is designed to eliminate camout and recess fallaway with elliptically based geometry and vertical sidewalls. [PREMIUM QUALITY]: High-strength chrome vanadium steel sockets provide superior torque for greater turning power with mirror chrome finish for corrosion resistance and S2 alloy steel bits reduce wear-outs and ensure longevity and the tamperproof bits are made of CrV for extra strength. [PRECISION]: Precisely machined bit tips ensure accurate size with a 0° drive angle that eliminates radial force preventing fastener recesses and gives access to nuts and bolts on European and Japanese cars and trucks. [INCLUDES]: Set includes 1/4" drive (4mm, 5mm, 6mm), 3/8" drive (8mm, 9mm, 10mm, 12mm, tamperproof 14mm) and 1/2" drive (tamperproof 16mm and tamperproof 18mm).