Amir Ziv-av, an inventor with Ziv-Av Engineering Ltd., Or-Yehuda, Israel, had developed a bidirectional (right or left-handed threads), variable-pitch screw with applications in mechanical and mechatronic devices.
The design starts with a thin-walled, flexible cylinder with "zero-pitch" threads. The threads basically form ridges around the cylinder. A longitudinal slit along the cylinder's entire length lets users apply a slight torque that realigns the ridges into right or left-handed threads, depending on the direction of the torque. Additional torque changes the thread from a single to a double.
The screw can be used with a locking nut that has teeth spanning a small arc on one side of the nut. This prevents the pitch from changing while the teeth of the nut lie across the slit in the screw cylinder. Alternatively, a nut with a slit similar to the cylinder's and with ridges or threads lining the hole can be used to lock the screw in place.
Possible applications for the variable-pitch screw include use as a bidirectional motion screw driven by a unidirectional power source such as a water or wind-driven turbine, or in a reversible screw conveyor in which the rotating screw is inserted inside a cylinder. It could also be used as a cable guide in winches to feed cable from side to side onto a spool. Such a device would cause less wear and be simpler than "moving-window" mechanisms found on conventional winches.