These are some simple files that might help some one build a mousetrap car. The first one is a CD adapter, so you can easily use a CD as a wheel with 8-32 threaded rod. These spin really concentric (previous years we used hand made nylon inserts which didn't work as well). The second file is a Mousetrap extender. Previously we used wooden dowels and zipties, and these work much better. It allows you to adjust the extension.