These wheels are designed to fit the "economy" or "low cost" plastic gear motors and is aimed at Mini-Sumo and small robots with rubber band tyres.This wheel was designed on Creo Elements, and printed on a Printrbot Simple Metal using Repetier Host with Slicer. These wheels are sized to fit #16 #31 or #72 rubbers bands with a 10% stretch. It's pictured with the #16 but some double sided tape may be required to stop them sliding off side ways... there's not real slip in rotation. The wider bands are more stable and less likely to roll off the side if pushed by an opponent. The Printrbot equipment was made available by Tanghall Smart Tech Club in York, England.