The Rack Jax Attachments allow for quick and easy attachment of the Rack Roller to a 3" wide pallet rack upright. The Jax attach to the top and bottom of either Rack Roller (M1200 or M4000) with two bolts each and stay connected to the Rack Roller. To mount the Rack Roller to the Pallet Rack upright, slide the 3" wide Rack Jax over the upright and pin using the two pins. This eliminates the need to bolt the Rack Roller to the upright. They are sold as a set of two. One set is needed per Rack Roller.