There is described a numbering system for carrying out numbering in a printing press comprising a numbering cylinder, a rotatable shaft defining a rotation axis, at least one supporting disc mounted on the rotatable shaft for rotation therewith, the supporting disc comprising a peripheral mounting ring for mounting of at least one numbering device (1.06; 2.06) on a periphery of the supporting disc, which numbering device (1.06; 2.06) is secured to the peripheral mounting ring (1.43) by means of a clamping mechanism. The peripheral mounting ring (1.43) has a T-shaped cross-section defining a pair of annular mounting grooves (1.43a, 1.43b) on each side of the peripheral mounting ring (1.43). The numbering device (1.06; 2.06) comprises clamping elements (1.50; 2.50) on each side of the numbering device (1.06; 2.06) which are adapted to cooperate with the annular mounting grooves (1.43a, 1.43b) for securing the numbering device (1.06; 2.06) onto the peripheral mounting ring (1.43). The clamping elements (1.50; 2.50) are preferably spring-loaded clamping elements.