A tool-holder column for a unit for converting a flat substrate that has two upper bearings (14, 16) each for supporting one end of an upper rotary tool (10), and two lower bearings (15, 17) each for supporting one end of a lower rotary tool (11), the flat substrate being movable longitudinally between the upper rotary tool (10) and the lower rotary tool (11), the bearings (14, 15, 16, 17) being vertically movable in opposite directions on either side of the longitudinal direction (L) of movement of the flat substrate, and a common drive for the bearings (14, 15, 16, 17) allowing the bearings (14, 15, 16, 17) to be moved simultaneously by one and the same distance in opposite directions, and including a screw device (25), the bearings (14, 15, 16, 17) being mounted one above another on the screw device (25) such that the rotation of the screw device (25) causes the linear movement of the bearings (14, 15, 16, 17) in opposite directions.