I got the Mustang for Christmas from my brother. A little more to them than meets the eye. The tire treads have to be shaped into a perfect circle so that the tabs and slots all match up. The underside of the car has to have the wheel wells shaped into the semi-circle again in a manner that the tabs and slots match up. I've spent most of my time looking around the house for items that are the same diameters so that I can accurately shape the metal. Turns out hobby knife handles were pretty much bang on.