An adjustable gripper system for releasably holding at least one sheet against a surface includes a pivotable gripper shaft with a pivot axis and at least one gripper having a gripper body defining a plunger cavity, the gripper body connected to the shaft for pivoting the gripper about the axis, a gripper plunger slidably disposed in the cavity and holding the sheet against the surface, and a cam follower actuated by a cam. The cam follower is connected to the gripper plunger to displace the gripper plunger along the cavity dependent upon a position of the cam. The system can be part of a sheet-collating pocket having a forward wall and a rearward wall pivotally connected thereto and, together, defining an opening for receiving the sheet, which can be part of a sheet-collating machine having the cam, a conveyor, at least one sheet feeding device, and many of the pockets.