Kelly bar is a key component of hydraulic rotary drilling rig, which simultaneously transmits the torque of the rotary drive and the pushing pressure of the pushing system to the drilling tool. Friction kelly bars are suitable for drilling in ordinary soil layers and have high drilling efficiency in softer formations.
The inner and outer key strips are easy to unlock, and the drilling rod lifting is relatively simple. Kelly bar generally composed of 5 drill rods, the drilling depth is generally deep.
Friction kelly bars rely on the frictional force between key bars to exert downward pressure, which is relatively small and not suitable for drilling in hard formations. Kelly bar consists of 2-5 telescopic tubular sections, with a standard square drill pipe having a total of 6 drive keys per section.

The interlock kelly bar is pressed downwards by the inner and outer key bar pressure surfaces, with high pressure, suitable for drilling in hard formations. The interlock kelly bar generally does not exceed four sections, and the drilling depth is within 80 meters. Before lifting the interlock kelly bar, it is necessary to unlock the inner and outer key bars before lifting the kelly bar, as unlocking is quite complex.