NSN 5305-01-521-0271

An externally threaded fastener whose threaded portion is of one nominal diameter, and whose unthreaded portion has been machined or ground in one or more places or over its entire length to a maximum diameter less than the minimum pitch diameter of the thread (excludes undercut for thread relief). It is no. 0 (0.060 in.) (1.5 mm) or larger, and is designed to be held or driven with either a wrench or inserted driver (excluding internal socket and multiple spline types) or both in sizes below no. 10 (0.190 in.) (5 mm) and larger sizes must have a head designed for any type inserted driver (excluding internal socket and 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. See also bolt, externally relieved body and bolt, internal wrenching.