Abstract: A device and method for repositioning sliders on profiled resiliently flexible zipper on bag sections of bag making material travelling along a manufacturing path. The device may comprise a frame, two movable rollers cooperatively opposed to one another mounted on free ends of arms which are pivoted and adapted for moving the rollers toward and away from one another. When the rollers are in close adjacency they are adapted to restrain the sliders for a predetermined interval while the zipper travels on with the bag making material whereby to reposition the slider properly with respect to transverse bag side sealing of the bag sections. The rollers are operable to shift the sliders in opposite directions along the zipper in the cyclical operation of the associated apparatus, whereby to test proper functioning of the sliders.