Abstract: Two parallel rails for the guidance of rollers or sliders on opposite edges of a panel, door or similar structural component comprise each a pair of elongated, substantially parallel members nestedly interfitted with a longitudinal internal clearance left therebetween to allow a change of their transverse separation and/or a limited relative tilting thereof. For this purpose the two members are joined to each other, at longitudinally spaced locations, by a plurality of adjustable connectors each comprising a male threaded element or bolt and a female threaded element or nut, each of these elements being anchored to a respective member. One member serves as a base, to be fixedly secured to a support, and the connector elements anchored thereto are nonrotatably held therein; the other member, forming a track, has a guide channel with an apertured bottom giving access to slotted or otherwise indented faces of the coacting connector elements to enable their rotation by a suitable tool such as a screwdriver.