Each bar has two precision broached holes, 45° on one end and 90° on the other end. Standard tool bits (H.S.S., CO., Carbide Tipped) are held firmly in place by a set screw. Bars can be held in boring tool holders, boring heads and drill chucks. Consisting of 1 each of 3/8", 1/2", 5/8", 3/4", 1" diameter bars on a fitted wooden block.