Long Forstner Hinge Boring Drill Bits 16mm - 25mmHigh hardness, rustproof, solid and durable. Self centering point, do not need assistant center drilling or center punching. Drilling and tapping in one, one step processing, greatly save processing steps and time costs, improve working efficiency. Spiral groove, within the processing thread, cutting up to exclude, and was curled applied internally threaded through holes. Wear and long life. Specification: Materials: high quality alloy Size: 16mm,