ITEM NAME:1 pcs Hex Shank Nitriding Black Spiral Groove Step Drill Bit Durable Steel.ï ¼Ë†2ï ¼â€°The central punch is not needed, small shaking, hard to be broken.Used with pistol drill or bench drill, water it to cool while working to prolong its life, the proper drilling speed is 250-400 rpm.
