5/16"-18 x 1/2", Grade 8 steel, External hex

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  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.

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  Flange bolts

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