HERE IS A SERIOUS PRODUCT STEEL STACKING PINS- MANY MAKE MISTAKE OF STACKING CONTAINERS WITHOUT LEAVING GAP. 2 REASONS IF ACCESSING TOP CONTAINER BY STEPS OFTEN THE DOORS HIT STEPS-SECOND REASON SAFETY. THESE PINS SIT INTO TOP OF LOWE CONTAINER AND INTO BOTTOM CASTINGS OF UPPER CONTAINER THUS RENDERING THEM SAFE. THESE STOP CONTAINER SLIDING BUT ADDED BONUS ALLOWS VENTILATION TO UNDER SIDE OF UPPER CONTAINER SO THE LOWER UNIT ROOF CAN DRY. THE FIRST IMAGES SHOW HOW THIS WORKS SIMPLE EASY FIT WWW.ISORISER.COM OUR PRODUCT.