Metallics G8HC34312 Bolts 3/4-10 X 3-1/2 G8 Hxbt St-zn (Box 25)

Go Grade 8 when the joint needs more tensile capacity than Grade 5 can carry. This bolt is medium carbon steel, heat treated, with 150,000 psi minimum tensile and 130,000 psi minimum yield, hardness Rockwell C33-39. Typical use is automotive and fleet work. If your load is modest and you want a more forgiving, less notch-sensitive fastener, Grade 5 is the usual choice.

Head width across flats measures 1.100 to 1.125 inch, so a 1-1/8 inch socket or wrench is the fit. Across the corners the head runs 1.240 to 1.299 inch, which is what you need to clear in a counterbore or tight pocket.

The finish is zinc over steel, which handles normal exposure and fleet service but is a sacrificial coating, not stainless. For constant wetting, salt spray, or chemical wash-down, expect the plating to give up over time. Note also that hot dip galvanizing or re-plating a Grade 8 bolt is not something to do in the field, since the base material is heat treated to Rockwell C33-39.

It ships as a box of 25, and 25 is the order minimum, so a single piece is not an option. Other sizes and quantities are available by request. The full box weighs 13.15 lbs.

Length is 3-1/2 inches measured from under the head to the tip, so that is your working figure for stacked material plus washers plus nut height. On a 3/4-10 bolt at this length, part of the shank will be unthreaded body, so plan for the thread to be engaged in the nut rather than inside the joint.

It is flagged Buy American compliant and ARRA compliant in the product record, with country of origin China. On a federally funded spec, confirm which clause your contract actually invokes, because the domestic-content test differs between Buy American and Buy America provisions.

Medium carbon steel in the AISI 1021 to 1045 range, heat treated to reach Grade 8 properties. That is the normal material band for a Grade 8 cap screw, and it is why the finished part sits at Rockwell C33-39 rather than the softer range of a Grade 5.