A hex cap screw is a cap screw with a hexagonal head, designed to be driven by a wrench.
An ASME B18.2.1 compliant cap screw has somewhat tighter tolerances than a hex bolt for the head.
Hex cap screws are fully threaded in shorter lengths (usually around up to 1-1/4 inch, depending upon the bolt diameter), and partially threaded with a shoulder beneath the fastener hex head in longer lengths.
Grade 8 Yellow zinc plated fasteners are heat treated and hardened for a more durable finished fastener