A ball screw is a clever tool that can take turning motions and change them into line movements. This happens without much friction, so only a small amount of energy is wasted. A further effect of this is that the inside of the ball screw wears very gradually. A ball screw is commonly larger than a leadscrew, because it has parts within the barrel. The ball screw nut holds some solid metal ball bearings which travel down the threaded interior of the barrel.

It is very important that it is impossible for particles of dirt to get into the ball screw interior. The ball bearings in the ball screw nut must be free to move along the shaft and the most miniature of particles can interefere with this. Ball screws are depended upon for being long-lived, and for being extremely accurate. Of course these advantages can be affected where obstructions gain entry to the casing. To prevent this the factory craftsmen are careful to use bellows and other methods so as to make certain that no tiny dirt specks stiking in the apparatus.

Ball screws can be extremely accurate because of the way in which they are created to close tolerances. Because of this ball screws are fitted in mechanisms that must be extremely precise, such as in robots, aircraft and missiles. Steppers incorporate them also, which are used to make semiconductors.
In some cases ball screws have the ability to functions backwards, a process known as back-driving. That is to say instead of inputting rotational motion and obtaining a linear movement as an output, the operator can also start out with a straight line movement and generate turning forces. It is possible to do this as a result of the low friction contained within the ball screw, which keeps the moving parts from seizing.