Left-hand thread direction, double hexagon head style, 0.312 inches maximum grip diameter, 0.500 inches maximum grip length, steel overall material, uns thread series designator

A high strength, 160,000 pounds per square inch (1100 megapascals) minimum tensile strength externally threaded fastener designed for use in applications involving great shear stress. The head is designed to accommodate an external wrench or driver. The head is not designed to be held or driven with an inserted driver, nor is it designed for rotation by the thumb and fingers. The unthreaded portion is of specific grip length, plated or unplated, and is machined to a tolerance of one thousandth (0.001) of an inch (0.025 mm) or less of a specific diameter for items one inch (25 mm) or less in diameter. Items over one inch (25 mm) in diameter shall have a tolerance of fifteen ten thousandths (0.0015) of an inch (0.038 mm) or less. The nominal major diameter of the threads shall be at least one thousandth (0.001) of an inch (0.025 mm) below the minimum shank diameter, but not below the minimum major diameter for applicable class of fit, as shown in the screw thread standards, fed std h28 and/or other nationally recognized standards. A locking feature may be incorporated in the design of the head or threads. See bolt, machine and bolt, clevis.