Linear guideways (standard ball version, needle roller & miniature versions) as well as a lightweight aluminium version are for precise linear movement and positioning. Four rows of hardened ball bearings (or rollers in the case of the linear roller rails) are in direct contact with the raceways of the hardened rails, plus the length of rail is sitting directly onto the supporting structure, so there is no bend in the rails. They are a highly accurate and repeatable system. As such, a pair of guides used together in parallel must be very accurately aligned for it to operate smoothly. For smaller strokes, please see our 'Linear Tables, Positioning Stages & Crossed Roller Sets' section.