Kelly-The kelly is the uppermost part of the drill stem. It is a hollow steel tube about 40 feet long with four or six sides. Mud Hose-The mud hose attaches to the mud pump at one end and attached to the drill stem at the other end. The drilling mud circulates through the mud hose. Crown Block-The crown block is a pulley located at the top of the oil derrick.
Steel cable is run over the crown block down to the traveling block.
This system of pulleys is used to raise or lower the drill pipe in and out of the well hole.