Screw-and-nut feed mechanisms

Full Title

Handling rods, casings, tubes or the like outside the borehole, e.g. in the derrick; Apparatus for feeding the rods or cables > Apparatus for feeding the rods or cables (E21B19/22 takes precedence; automatic feed E21B44/02); Apparatus for increasing or decreasing the pressure on the drilling tool; Apparatus for counterbalancing the weight of the rods > Screw-and-nut feed mechanisms