| 摘要 |
<p>In a drill rod for a drilling machine, the rod outer diameter has a large diameter almost equal to the drill hole diameter, an a male thread is formed at one end and a female thread at the other end, with at least one small diameter portion adjacent the female thread. This step tube rod is capable of reducing the bending of holes. Further, a drilling machine using this step tube rod facilitates the positioning of the drill rod and is capable of efficiently and safely effecting the connecting and recovering operation.</p> |
