Abstract: A belt (1), suitably closed into ring-shape and carried around at least two turn-round and/or driving cylinders (2, 3), is made of plastics material, particularly of polytetrafluoroethylene, or the like, or it is constituted by a fabric, particularly of glass, impregnated and/or coated with plastics material, particularly with polytetrafluoroethylene. Both longitudinal edges of the belt have an enlarged guiding bead (6) resting on the edge (4) of each end face of the turn-round cylinder and/or driving cylinder (2, 3) or on an annular step of said cylinder, or engaging into an annular groove in said cylinder. The enlarged guiding bead (6) may be constituted by a flexible core (5) incorporated within the respective longitudinal edge of the belt (1), and particularly enwrapped by a marginal portion (101) of the belt (1) which is folded over around the core (5) and is secured to said belt (1).