Type: 0.7 inch (19 mm); Material: Made of high quality ABS plastic with excellent durability, excellent toughness and abrasion resistance, and is highly resistant to chemical and heat and is a superior material among plastic resins. | Sleeves: Parts for attaching shelves, wire bars, and U-shaped bars to poles. | Sleeve is "wedge" construction The more the load is applied, the four corners of the shelves tighten the sleeves and add strength. | HOW TO USE THE SLEEVES: The sleeves are made of resin and have a trapezoid cylindrical shape. It is divided in half, so you can snap it together and attach it to the pole. |Finally, slide the sleeve downward and hear a "click", the sleeve will stay firmly in the groove of the pole.