API 7-1 Square & Hexagonal Kelly for Oilfield drilling

Kelly is located in the top of the drill string, with square and hexagonal. In rotary drilling, when it is drilling, kelly connected with square bushing and rotary bushing, transfer the ground rotary torque to drill pipe and to drive the drill bit,bearing the weight of the drill string.In the drilling of the turbine and screw, the weight of the drill string and the counter torque are supported.