This listing is for a set of (4) NEW CW3 U groove wheels. These wheels are manufactured with 2 integrated bearing. The bearings have a 8mm center bore, meaning you can replace the wheels on most dollies that use skate/skateboard wheels. This will allow you to use your dolly on any uneven surface with the help of some pipes. As seen in some of the pictures, these will run best on a pipe with an outside diameter between 15mm and 0.8 inches (22mm) . The outside diameter of the wheel is approximately 1.75 inches (45mm) in height and about 7/8 inches (23mm) in width. If you’re planning to build your own dolly, you can also use a 5/16″ bolt instead of a 8mm. Check CamOnWheels on Facebook for more ideas and promotions. Any questions, please ask before you buy The listing is only for a set of (4) U groove wheels so the pipes and screws are not included.