The Rio Craft Dry Box Shim Kit allows you to add a flip seat or captains chair over any Rio Craft Drybox. Simply screw the shim kit onto the hanger tabs of your Rio Craft Drybox, which will add 3/4" of space between the box and your frame to allow clearance for a flip seat (sold separately). You will need to increase your bay width approx 1.5" with this shim kit. Will only work on Rio Craft Dryboxes.