Medium carbon steel, quenched and tempered in accordance with SAE J1199 material requirements and ANSI/ASME B18.2.3.1m dimensional tolerances. Compatible with class 8 hex nuts, all metal lock nuts or nylon insert locknuts. Metric mild-steel or hardened flat washers as well as helical spring lock washers may also be used with these cap screws for a complete assembly. Cap screws are zinc clear finish.