2a thread class, right-hand thread direction, 0.156 inches minimum thread length, 0.281 inches minimum and 0.283 inches maximum fastener length, flat chamfer head style, 0.250 inches nominal head diameter

An externally threaded fastener whose threaded portion is of one nominal diameter, no 0 (0.060 in.) (1.5 mm) or larger. It has a round unthreaded neck or shank all or part of which is of greater diameter than the threaded portion. The head is designed to be driven with either a wrench or an inserted driver or both in sizes below no. 10 (0.190 in.) (5 mm) nominal diameter. No. 10 (0.190 in.) (5 mm) and larger sizes must be designed for any type of inserted driver, but may also provide for external wrenching of the head. A locking feature may be incorporated in the design of the head or threads. For items which are both shouldered and have an externally relieved body, use screw, externally relieved body. For items with a no. 10 (0.190 in.) (5 mm) or larger thread diameter without an inserted driver head, use bolt, shoulder. Excludes:bolt, internal wrenching and screw, cap, socket head.