Square Filter Holder for Open-source Optics

This is a filter holder for optical experiments.

This component is part of the [Open-source optics project](http://www.appropedia.org/Open_source_optics), whose goal is to radically reduce the cost of scientific optical hardware: by the [Michigan Tech's Open Sustainability Technology Research Group](http://www.appropedia.org/Category:MOST).

For similar see the [Open-Source Lab How to Build Your Own Hardware and Reduce Research Costs](http://www.appropedia.org/Open-source_Lab)