短语词组短语roller r bit 牙轮钻头roller bearing bit 滚柱轴承钻头roller cone bit 牙轮钻头roller cutter bit 牙轮钻头cross roller rock bit 十字形四牙轮钻头sealed roller bearing bit 密封滚动轴承钻头roller core bit 取心牙轮钻头roller -bit hole rig 牙轮钻机 返回 roller bit