Machinery and fabricated structures for use in the production of oil, gas, water, and other fluids from subterranean wells and for the drilling of such wells, namely, rig structures, namely, [ derricks, drilling masts being parts of machines, ] drilling rigs, [ drill floors for use with drilling rigs, workover rigs used for the repair or stimulation of production wells, off shore and ] on shore drilling rigs [, operator cabins for use with drilling rigs, hoisting machinery, namely, cranes, machines for erecting tubular goods for oil, gas, and water wells, machines for handling tubular goods for oil, gas, and water wells, machines for loading tubular goods for oil, gas, and water wells, drawworks, namely, machines for reeling out and reeling in the drilling line; top drives, namely, machines for turning the drillstring; pipe elevators, power slips, namely, self-gripping toothed devices used to grip components of a drilling rig; iron roughnecks, namely, tubular handling machines for oil, gas, and water wells; rotating machinery for rotating equipment and tubular goods; pipe handling machinery for bringing tubular goods to and from the drilling rig; fluid handling machinery and solids control machinery, namely, shale shaking machines, mud pumps, mud cleaners, namely, machines for separating solids from fluids; degassers, namely, machines for separating air or gases from drilling fluids; desilters, namely, machines for separating fine and ultrafine solids from fluids; desanders, namely, machines for separating solids from fluids; cones, namely, parts of machines used for separating solids from fluids; mud agitators, namely, machines use to maintain uniform consistency of fluid in a mud system; mud hoppers, namely, parts of machines used to add drilling fluid additives to a mud system; mud guns, namely, parts of machines used to maintain uniform consistency of fluid in a mud system; mud mixers, valves being parts of machines, namely, relief valves, float valves and gate valves ]