NSN 5305-01-331-0021

An externally threaded fastener whose threaded portion is of one nominal diameter, no 0 (0.060 in./1.5 mm) or larger, designed to be held or driven with either a wrench or an inserted driver or both (excluding internal socket or internal multiple spline types), in sizes below no. 10 (0.190 in./5 mm). No. 10 and larger sizes must have a head designed for any type inserted driver (excluding internal socket or internal multiple spline types), but may also be designed for external wrenching. A locking feature may be incorporated in the design of the head or threads. Excludes bolt, clevis; bolt, externally relieved body; screw, externally relieved body; and screw, assembled washer. See also, screw, instrument; bolt, machine; bolt, internal wrenching; and screw, cap socket head.