3.5mm Ball Chain Sprocket

Sprocket for 5mm stepper motor shaft (with flat) for use with a 3.5mm ball chain. Intended for use with a polargraph

http://www.polargraph.co.uk

This design wont slip when its contacting as little as 90 degrees of the sprocket, or as few as five links in the chain.

Derived from both:
http://www.thingiverse.com/thing:28811
http://www.thingiverse.com/thing:12403
Thanks for the inspiration.