Metallics G8HC58412 Bolts 5/8-11 x 4-1/2 G8 HXBT St-zn (Box 25)

It's a 5/8-11 coarse thread bolt, 11 threads per inch, so it mates with standard 5/8-11 UNC nuts and tapped holes. Measured shank diameter runs 0.6170 to 0.6250 inch. If the hole in your steel is tapped 5/8-18 fine, this bolt will not thread in.

Grade 8 here means 150,000 psi minimum tensile and 130,000 psi minimum yield, with a hardness of Rockwell C33-39. That's a real step up from Grade 5, which is why these get used where a Grade 5 cap screw won't carry the load, like fleet and automotive work and heavier equipment anchoring. Same 5/8-11 thread, so it drops into the same tapped hole or nut as a Grade 5 of the same size.

No. The G8HC58412 is not Buy American compliant and is not ARRA compliant, with country of origin listed as multiple. If your contract carries domestic sourcing language, this part will not satisfy it.

The plating is zinc over steel, which handles indoor and sheltered conditions and gives moderate protection in damp mechanical rooms. For direct weather exposure, standing water, or coastal air, zinc plated Grade 8 is not the right pick; go to hot dip galvanized or stainless, keeping in mind stainless won't match the 150,000 psi tensile of Grade 8.

These 5/8-11 x 4-1/2 Grade 8 hex bolts ship boxed, 25 to the box, with an order minimum of 50 each. So the practical buy is two boxes. Other sizes and quantities can be requested.

Material is medium carbon steel in the AISI 1021 to 1045 range, quenched and tempered to Grade 8 hardness of Rockwell C33-39. Heat treated medium carbon steel loses its strength when welded, so use these as bolted fasteners only, not as weld studs.

Field application covers the electrical, plumbing, heating and air conditioning trades, so these are commonly used for strut, trapeze, and equipment mounting where a Grade 5 won't carry the load. The automotive and fleet reference is about the strength class, not a limit on where they can be used.

The 4-1/2 inch length is measured under the head, so that is the full amount available to pass through your material plus nut and washers. Head height of 27/64 inch sits above the surface and does not count toward grip. For a 5/8-11 bolt you want at least a couple of threads protruding past the nut once everything is stacked.