Linear bearings are used in applications where a component needs to be moved along a straight line with high accuracy. The object may also need to be returned to its origin with high repeatability.

Linear bearing rails provide a smooth, precision, guiding surface on which the rolling element of a linear bearing rides. They are an integral part of linear bearings, typically ordered separately ...

In the early days of 3D printers, most builds used smooth rods and bearings that rode on them. But these days, printers are shipping with either V-slot extrusions with Delrin wheels or linear rails.