Internal coolant hole for each piece, guarantee processing reliability and longer service life U drill can be directly processed on the workpiece without drilling guide holes in the center Using indexable insertssaves material than the whole hard drill, and the consistency of the insertsis easier to control the size of parts. The rigidity of U-drill is good, it can adopt a high feed rate, and the diameter of U-drill is much larger than that of ordinary bit. The diameter is from 13MM to 60mm, step by 0.5mm