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. The length of the threaded portion of the shaft on standard hex cap screws is 2 times the diameter of the shaft plus 1/4 inch. So therefore short hex cap screws may be fully threaded or nearly fully threaded; long hex cap screws may have large portions of smooth unthreaded shaft above a shorter threaded section. SRI primarily stocks Grade 8 fasteners made of medium carbon alloy steel, quenched and tempered. Our bolts are plated with yellow/zinc dichromate for excellent corrosion resistance. Grade 2, Grade 5, Metric, Stainless and Metric Stainless fasteners are available upon request.