Abstract: A carriage, preferably carrying a knife for cutting a moving web for attachment of the cut web end to a web winding roll, is driven on a supporting rail along a linear path by means of a driving motor operating a toothed driving belt. The belt is detachably clamped to the carriage by a clamp fixed on the carriage and formed by a support plate having a belt supporting surface thereon and a pressure plate provided with teeth for mating engagement with the belt teeth mounted on the support plate in opposed relation to the support plate surface to define with the surface a slot for reception of the belt. The pressure plate is slidably supported for movement toward and away from the surface and is spring-biased to normally clamp the belt therebetween.