Top drives are suspended mechanical drives that provide torque to the drill string and serve as an alternative to the use of a Kelly drive or rotary table. They are suspended bellow the traveling block at the swivel joint and move up and down the derrick as controlled by the draw-works. Top drives require less manual labor and have replaced rotary tables or Kelly drives as they can accommodate longer sections of drill pipe, referred to as a double or triple. Top drives consist of one or more electric or hydraulic motors and are connected to the drill string by a short section of pipe that is referred to as the quill.
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