The clamp post mount with 38mm (1.5 inch) ball is designed for wide range clamping. The heavy-duty mount is made of high-strength composite materials with corrosion-resistant stainless-steel hardware. The clamp mount opens to 2.75 " diameter to securely grip roll bars, tubes, handlebars, warehouse carts, etc. The 38mm ball (1.5 inches) is compatible with 38mm (1.5 inches) shafts.