Metallics RM147SLT 5/16-18 x 5 in. Round Head Slotted Machine Screws - Steel Zinc - Each

It's a 5/16-18 UNC thread, 18 threads per inch, in a 5 inch length. That's the coarse thread series, so it mates with standard 5/16-18 nuts, tapped strut, and threaded inserts. Fine-thread 5/16-24 hardware will not engage it.

Tensile strength is 60,000 psi minimum with a hardness of Rockwell B70-B100. That is low carbon commercial grade, equivalent in strength class to common unhardened machine screws, not a Grade 5 or Grade 8 bolt. Use them for mounting boxes, panels, straps, and equipment. For a structural or high-clamp-load connection, step up to a graded hex bolt.

Metallics lists the RM147SLT as both ARRA compliant and Buy American compliant, with country of origin recorded as multiple. If your spec requires a single-country certification on file, request the mill documentation with the order.

Material is zinc plated steel, AISI 1006-1022 low carbon. Zinc plating handles indoor and sheltered service, damp basements, mechanical rooms, and interior electrical enclosures. For sustained outdoor exposure, washdown areas, or coastal sites, specify stainless steel instead.

They ship boxed in a count of 100, which is the order minimum. Plan on a full box per order rather than loose pieces.

Metallics targets these at the electrical, plumbing, heating and air conditioning trades. The 5 inch length is for through-bolting thicker assemblies, mounting equipment through strut and spacers, or reaching through insulation and standoffs where a short screw bottoms out. The round head sits proud rather than flush, so no countersink prep is needed.