From original post on Thingiverse (https://www.***********.com/thing:102800):
Summary
Room for a micro servo (like a sg90) and an ultrasonic sensor (like HC-SR04).
Designed to be mounted on humanoid robots like bioloid.
Yo can find the .scad for this file here:
http://code.google.com/p/droide/source/browse/#svn%2Ftrunk%2Fprintable%20parts%2Fhead