Kelly
Kelly is a steel tubular with hexagonal or square profile. It is connected between swivel and drill string. Kelly acts as a conduit for drilling fluid to be circulated from mud pump through drill string. Kelly passes through the kelly drive bushing with matching profile. Kelly drive bushing sits in the master bushing of the rotary table. The square or hexagonal profile of the kelly locks it in with the drive bushing and helps in transmitting rotary motion of rotary table to the drill string through kelly.