5/16" x 1-3/4", Zinc plated steel, External hex

Screws with large threads for use in sheet metal sometimes also used in plastic, fiberglass or wood.

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

Large wood screws technically called lag screws.