A gripper mechanism (10) for mounting a sheet (22) on a drum (20) in a printing machine, the mechanism comprising: a holding element (16) movable between a holding position at which the holding element secures the sheet to the drum and a release position at which the holding element does not secure the sheet; and a magnetic holder (24, 26) which provides a relatively large force to hold the holding element (16) at the holding position and which provides a relatively small force to urge the holding element to the holding position when it is removed from the holding position.
