The expansive bit makes it possible to drill a full range of diameter holes with the same bit.Adjustable using a screwdriver or wrench.Made of drop-forged tool steel in one piece, heat treated all over. Head and adjustable cutters hardened and tempered.Locking screw zinc plated with hexagonal head with slot.Sizes 15 to 45 mm & 22 to 76 mm, both with round shank