Metallics JSHC51634 5/16-18 x 3/4 in. Socket Head Hex Cap Screws - Alloy Steel Black - Each

They are 5/16-18 by 3/4 inch long, a UN thread form at 18 threads per inch. That means they thread into any standard 5/16-18 tapped hole or nut, and the 3/4 inch length is measured under the head since a socket head cap screw seats flat.

Size the counterbore off the published head dimensions: the head measures 0.457 to 0.469 inch across and 0.306 to 0.312 inch tall. Allow clearance over 0.469 inch for the bore diameter, and at least 0.312 inch of depth to bring the head flush. These conform to ASME B18.3-2012, so standard counterbore tooling for 5/16 socket heads applies.

Yes. The alloy steel socket head delivers higher tensile strength than equivalent sizes of Grade 5 or Grade 8 hex head cap screws, rated at 180,000 psi minimum tensile and 162,000 psi minimum yield. Because it is internally wrenched with a hex key, it also needs less surface area or counterbore clearance than a hex head of the same diameter, which matters in tight brackets and machined pockets.

No. The JSHC51634 is not Buy American compliant and is not ARRA compliant, and country of origin is listed as multiple. If your project carries a domestic-sourcing clause, this fastener will not satisfy it.

A hex key. The JSHC51634 has a socket head with an internal hex drive, so it is driven from inside the head rather than with an open-end or socket wrench on flats. Plan for hex key or hex bit access directly above the fastener.

Treat them as an indoor or protected-location fastener. The material is alloy steel with a black finish, which is not a corrosion-resistant plating like zinc or stainless. For exterior, damp, or washdown environments, specify a zinc-plated or stainless fastener instead.

They ship in a jar of 100, and 100 is the order minimum. If you need another size or a different count, Metallics offers other sizes and quantities by request.

Hardness is Rockwell C39, which is well above typical aluminum or mild steel. In a soft tapped hole the threads in the base material will strip before the screw yields, so size your thread engagement accordingly rather than relying on torque alone. Ductility is still there: minimum 10 percent elongation and 33 percent reduction of area on machined specimens.

They are stocked for the electrical, plumbing, heating and air conditioning trades: mounting panels and enclosures, strut and bracket connections, equipment and machine assembly where a high-strength internally wrenched fastener fits in a counterbore. The 180,000 psi minimum tensile rating is why they turn up on equipment mounting rather than general sheet metal work.