Metallics G8HC340 Bolts 3/4-10 X 2-1/2 G8 Hxbt St-zn (Box 25)

The G8HC340 is a 3/4-10 hex cap screw: 3/4 inch nominal diameter with 10 threads per inch, which is standard UNC coarse thread for that diameter. Measured shank OD runs 0.7410 to 0.7500 inch. It mates with any 3/4-10 UNC nut or tapped hole, so pair it with a Grade 8 or Grade C nut to use the bolt's full strength.

Yes, Grade 8 is the higher strength of the two. The G8HC340 is rated 150,000 psi minimum tensile and 130,000 psi minimum yield, with hardness of Rockwell C33-39. Grade 5 tops out well below that, which is exactly why this bolt is used in automotive and fleet work where Grade 5 will not carry the load. Dimensions are the same, so it drops into the same 3/4 inch hole, but match it with a Grade 8 nut or the nut becomes the weak point.

Across the flats the hex head measures 1.100 to 1.125 inches, so a 1-1/8 inch socket or wrench is the right size. Across the corners it runs 1.240 to 1.299 inches, which matters if you are checking clearance in a tight pocket.

It is zinc plated medium carbon steel. Zinc plating handles indoor service and general shop and fleet use well, but it is a sacrificial coating, not stainless. For sustained weather exposure, marine air, or chemical washdown, step up to a hot dip galvanized or stainless fastener instead. Note that Grade 8 strength is not available in standard stainless, so if you need both the strength and the corrosion life, specify galvanized Grade 8.

The G8HC340 ships as a box of 25 and the order minimum is 25 count, so 25 pieces is one unit, not a loose-piece item. Box weight is listed at 8.97 lbs. Metallics does make other sizes and quantities in the G8HC and JG8HC series available on request.

The record flags the G8HC340 as both ARRA compliant and Buy American compliant, with country of origin listed as China. If your contract carries a strict domestic-melt-and-manufacture clause rather than the ARRA/BAA treatment, have your specifier confirm which standard applies before you submit it.

Head height runs 0.455 to 0.483 inch, so plan on roughly half an inch of stand-off above the clamped surface plus room for the socket. If you need a flush or low profile result, a hex cap screw is the wrong head style for the job.

Medium carbon steel in the AISI 1021 to 1045 range, quenched and tempered to reach Grade 8 properties. That heat treatment is what gives the 150,000 psi tensile rating, and it is also why you should never weld or re-heat one of these bolts: heat kills the temper and drops it below Grade 8.