Helical Spring Lock Washers ASME B18.21.1

Helical spring lock washers, commonly called split lock washers or helical lock washers, are open-ring washers with a helical twist that leaves the two ends at different elevations. Positioned beneath a nut or bolt head, they exert spring force as the joint is tightened and offer a hardened bearing surface. Unlike flat washers, which primarily distribute bearing load, helical spring lock washers have a split, raised profile. They are also distinct from tooth lock washers, which use internal or external teeth to engage the bearing surfaces of a joint.

ASME B18.21.1 specifies dimensional requirements, physical properties, and related test methods for inch-series helical spring-lock washers. The standard includes regular, heavy, extra-duty, and high-collar series, with differences in geometry and dimensional requirements. The appropriate series depends on the joint design, mating fastener size, and available clearance.

These washers are used in general mechanical assemblies, industrial equipment, and maintenance applications where a helical spring-lock washer is specified. However, the term lock washer does not guarantee that a fastened joint will resist loosening under every service condition. Vibration, joint design, and retained preload must also be considered when selecting a fastening arrangement.