Cheshire collimator for newtonian telescope

This eyepiece is used to collimate your newtonian / printonian telescope's primary and secondary mirrors.

Inspired by this laser collimator,
http://www.thingiverse.com/thing:12624
but here there is no need to collimate the collimator ;-) .

Use: several tutorials online, I especially like this one:
http://www.astro-baby.com/collimation/astro%20babys%20collimation%20guide.htm
check also this:

http://www.atmsite.org/contrib/Carlin/collimation/kolli2.htm#mkcombination

and

http://