Abstract: A kit for retrofitting retarding roller conveyors having a plurality of retarding rollers, each having an outer cylindrical surface of a given diameter, the retarding rollers being arranged parallel to each other, transversely between opposite sides of a frame, each retarding roller being rotatable about a rotation axis and spaced apart from each other by a distance measured between the outer cylindrical surfaces of adjacent ones of the retarding rollers, the kit having a plurality of roller elements, two roller elements being fitted on each retarding roller, each roller element having an outer cylindrical surface of a diameter greater than the outer cylindrical surface of the retarding rollers; and a plurality of timing belts, one timing belt extending between and thus interconnecting two adjacent retarding rollers.