This was a project that I have been working on for a few months on an off. The wheels are a little larger than 2 inches ind diameter. The are designed to be used on the Tamiya 3mm shaft gearboxes. These where the ones that where featured on the Make: website. http://blog.makezine.com/archive/2010/04/3d-printable_mecanum_wheel.htmlThere are two versions of the .STL The one that ended in inches is the one I used for the 3d-print. The other one should be in millimeters. For some reason the file size is different.The .STl files are large. Download the zip file not the .STLPrint using a commercial Printer such as a Dimension SST. Assemble using a 3/32 brass rod or tube.