A leadscrew (or lead screw), pronounced /liːd skruː/, also known as a power screw or translation screw, is a screw used as a linkage in a machine, to translate turning motion into linear motion. Because of the large area of sliding contact between their male and female members, screw threads have larger frictional energy losses compared to other linkages. They are not typically used to carry high power, but more for intermittent use in low power actuator and positioner mechanisms. Leadscrews are commonly used in linear actuators, machine slides (such as in machine tools), vises, presses, and jacks. The word "lead" – pronounced /liːd/, from the verb "to lead" – refers to the amount of distance travelled per rotation, not the metal.

Leadscrews are manufactured in the same way as other thread forms: they may be rolled, cut, or ground.

A lead screw is sometimes used with a split nut (also called a half nut) which allows the nut to be disengaged from the threads and moved axially, independently of the screw's rotation, when needed (such as in single-point threading on a manual lathe). A split nut can also be used to compensate for wear by compressing the parts of the nut.

A hydrostatic leadscrew overcomes many of the disadvantages of a normal leadscrew, having high positional accuracy, very low friction, and very low wear, but requires continuous supply of high-pressure fluid and high-precision manufacture, leading to significantly greater cost than most other linear motion linkages.

Power screws are classified by the geometry of their thread.

V-threads are less suitable for leadscrews than others such as Acme because they have more friction between the threads. Their threads are designed to induce this friction to keep the fastener from loosening. Leadscrews, on the other hand, are designed to minimize friction. Therefore, in most commercial and industrial use, V-threads are avoided for leadscrew use. Nevertheless, V-threads are sometimes successfully used as leadscrews, for example on microlathes and micromills.

Square threads are named after their square geometry. They are the most efficient, having the least friction, so they are often used for screws that carry high power; however, they are also the most difficult to machine, and are thus the most expensive.

Acme threads have a 29° thread angle, which is easier to machine than square threads. They are not as efficient as square threads, due to the increased friction induced by the thread angle. Acme threads are generally also stronger than square threads due to their trapezoidal thread profile, which provides greater load-bearing capabilities.