in one embodiment , a conveyor comprises identical carriages and apparatus for connecting the carriages end - to - end . the carriages each include first wheel pairs supported for a rotation about spaced apart parallel axes and a second wheel pair supported for rotation about a perpendicular axis . the first and second wheel pairs are rotatably supported by self - lubricated bearings . the connection apparatus may comprise either connection rods or a wire rope . in another embodiment , the conveyor comprises identical links each including first and second link portions . the link portions are pivotally interconnected by a first connecting pin which also supports a first pair of wheels . adjacent links are interconnected by a second connecting pin which also supports a second wheel pair . the first and second wheel pairs are rotatably supported by self - lubricated bearings .