Hex head cap screws or hex bolts have a hexagonal head that is designed for a ratchet or spanner torque wrench.  This allows for tightening of the screw.  Hex cap screws or hex bolts are manufactured with different grades, finishes, sizes, and specifications depending on application.  A washer is commonly used under the head of the hex cap screw and the chamfered end and a nut is used matching up with the thread type of the hex bolt to exact specifications.  These fasteners are mostly used in construction, machine parts, and maintenance.