These are the parametric version of the gear wheels that are being used in the caterpillar robot that I'm deisgning with Dannynoc here

http://www.thingiverse.com/thing:7752

The parameters that define the piece are explained in the scad file.
In the example that I've uploaded,I've added some holes in order to fix this wheel to a futaba servo.

Added the parametric links in case someone wants to print them with the wheel.
They are a derivatie work of http://www.thingiverse.com/thing:7209

Just download the scad file, read what the parameters represent and have fun =)