This is part of a system of prints that turns an Open Beam into an optical rail. An optical rail is a long, straight, sturdy rail onto which optical components such as light sources and lenses can be bolted down and easily shifted along the length of the rail.
Commercial optical rail sells for $115/ft. Open beam only costs $10/m or $12/m for the fancy black anodized stuff. You get the idea.
This component is part of the Open-source optics project, whose goal is to radically reduce the cost of scientific optical hardware: by the Michigan Tech's Open Sustainability Technology Research Group.