Upper- and lower rails (2, 3) are formed from a metal strip with low-friction coating. The geometry of their profiles is partially-surrounding and resists detachment. As a result of contour oversize, the upper rail is pre-tensioned against the lower rail.

The upper and lower rails (1a, 1b) have the same geometry and can be slotted together in a reverse mirror image arrangement in which they are separated by ball bearings (12). The upper rail (1a) moves on balls along the lower rail (1b).