The Kelly is made of 4145H chromium molybdenum steel and carried out upon standards such as API Spec 7-1,NS-1. It can transfer the torque of the turntable to the drill pipe, provide power for the entire drill string, drive the drill bits to rotate, and bear the weight of the drill string. The Kelly total length is generally more than 12 meters.

 According to the appearance can be divided into square and hexagonal kelly.