This is a Customizable version of http://www.thingiverse.com/thing:28143 
I have lots of different generic motors, and I need them for a couple of projects that involve the Arduino. In order to make the motor less ugly and more capable of being screwed on to something, I made a parametric case, so that I could put in the parameters, and get a case for any of my motors. Then I realized that other people might need a motor case too, so I put it on Thingiverse under public domain. It also comes with 2 example motor case, for the motors shown in the pictures. 
(It is not physically tested yet, although it has been theoretically tested) 
Update: 7/27/2013 
Now you can change the resolution for better prints and faster rendering!