To maintain parallel rails and fill gaps between the rail and your compatible cart.
First, select your cart frame type. Then select the shelf system you plan to use. You will be prompted with the correct spacer kit needed.
These spacer kits are not required, but we highly recommend using for most setups.
Without spacer kits on most cart/shelf combinations, the rails will not remain parallel, and/or the mounting rods will protrude from the rail end blocks.
See 90º Conversion kit for these cart users:
Gravity CART M 01 B