Abstract: The invention relates to an assembly comprising a rolling device and two parallel guiding slideways, in which the slideways (1, 2) are constituted by cylindrical elements of different diameters. The rolling device (3) comprises an axle of rotation (4) perpendicular to the plane of the two slideways and mounted displaceably parallel between these latter, a central roller (5) mounted freely rotatably on the axle and whose diameter is such that its periphery will be in rolling contact with the slideway (2) of smaller diameter, but out of contact with the other slideway, and two outer rollers (6) freely rotatably mounted on the axle of each side of the central roller, and whose peripheral internal surface comprises a concave groove (10) in rolling contact with the slideway (1) of greater diameter, but out of contact with the other slideway. This assembly may be used particularly in lighting apparatus.