• Inner diameter 18mm, outer diameter 50mm About Sizes. - Wide range of sizes: The Anti-Sink Rubber Ball's inner diameter 18mm
• How To Install. - Press hard to install; Pull hard to remove.
• Design Features. - Anti-Sink and Anti-Slipery features; Design for uneven or slipery floor surfaces; Such as sand, grass, cement, rock, mud, tile, rug, wood floor, and etc. Can be used indoor and outdoor; Could attach on chair, table, and cot; Easy to carry in the package while camping, hiking, cycling, fishing, and different kinds of activities.
• Other Features. - Made of rubber material; Easy to wash and clean; Portable, could be stored in the mesh sport bag, which comes with the rubber balls. 4 ball total weight: 7oz/200g.
• Notice. - If not sure about the sizes, you may check the video before choose.