Zinc plated grade 8 steel, 5/16"-18, US

US Fasteners

Hex bolt

Hex bolts

Bolts with hexagonal heads and machine threads for use with a nut or in a tapped hole. Also known as hex cap screws or machine bolts.
Flange bolts

Flange bolts

Flange bolts have a flange on the bottom of the head that distributes the load like a washer.
Nut

Nuts

Nuts have internal machine threads, for use with machine thread bolts and screws.