Abstract: A cut off, cross perforator or scoring cylinder having a quick relese mounting for a cross-cutting or perforating blade is disclosed, hereafter called cylinder. The blade is mounted in a longitudinal groove in the periphery of the cylinder. It is held in place against a side wall of the groove by means of a retaining bar which is disposed within the groove. The retaining bar is normally urged against the blade by compression springs. In order to change blades, the retaining bar is pivoted away from the blade by means of an operating lever having pins insertable in openings in the outer wall of the retaining bar. This frees the blade for removal and enables insertion of a new blade. Endwise clamps are provided with resilient pads interposed between the clamps and the retaining bar to support the retaining bar against dislodgement while permitting pivotal movement thereof.