... and long life with meeting the requirements of drill hole. For rock drilling with drill rod in person’s hands, H22 and H25 ... is 55SiMnMn, 95CrMo.etc; For rock drilling of drifting, we choose the drill rods such as the drill rods with hexagonal cross section ... and different-diameter and quick-change drill rods (H25,H28、H32,H35) generally. For rock drilling for production (underground mining and ...