Windup Walker Negative
Description
This is a negative space object that can be used to do a boolean difference on other models to cut a slot and attach windup walker legs.
Instructions
Get windup walkers from store.makerbot.com/makerbot-windup-walkers.html
License
Windup Walker Negative by tbuser is licensed under the Attribution - Share Alike - Creative Commons license.

It should be noted that tinkercad now allows you to do .STL import. So, you could very easily build up something there, import this negative shape, assign it the "hole" color, and re-export to .stl. Very cool!
as in http://tinkercad.com