1. It is used to drill soft ground,base rock,and floppy precipitated stratum upper
ground water.
2. It is easy to yank the bit so as to homoloze the change of terrane.
3. It is easy to be able to drill with its broad aperture and depth thanks to
developing diverse model.
4. It is easy to be able to homologize the diverse change of terrane thanks to
developing diverse...