The DEWALT TSTAK™ Caddy has a tough, durable design made from 3mm polypropylene plastic. Stores up to 5 TOUGH CASE+ accessory cases and 4 small bulk storage cases (Tic Tac). The TSTAK™ interlocking storage system allows toolboxes to be interconnected and configured to meet the user's needs. Engineered plastic side clips to enable numerous boxes to be stacked and held securely together for transport.