NSN 5305-01-255-2601

An externally threaded fastener whose threaded portion is of one nominal diameter. It may have an unthreaded portion with a diameter less than, equal to, or greater than the diameter of the threaded portion. It has either a vertically flattened, circular knurled, or wing type head, all of which are designed for rotation by the thumb and fingers. For items having wrenching facilities such as socket recess, multiple spline or slot heads, use screw (as modified) or bolt (as modified).