The most common cap screw is the hex cap screw. This cap screw is a headed and externally threaded part designed for insertion through a close tolerance internally tapped hole and mated with a nut. Tension is induced by rotation of the cap screw head. There is often a washer forged under the head. The point at the threaded end of the cap screw is machined flat so it will fit into a drilled hole. Cap Screws usually have closer tolerances than do bolts.
Serrated hex flange bolts have a ridge or skirt (flange) around the bolt head that distributes the clamping load when the bolt is tightened. The flange works like a washer. Flange bolts are sometimes called frame bolts.
Slotted flat cap screws have a flat top surface, milled slot, and a conical bearing surface with a head angle of 82°. They are used for assembling close tolerance machinery where head clearance is critical.