This is a lens holder for a lens that is 50 mm in diameter. A semicircular slot 3 mm wide holds the edge of the lens. Adjust the SCAD file for the lens and mounting hole dimensions you need . Lens holders are useful for demos and optical experiments. The specific lens shown in the photos is "50mm Optical Glass Lens Collimator Plano-Convex for Led Projector" which is Ebay item 161126916191. On my printer, the slot ended up at 2.7 mm wide, about 0.3 mm too narrow for the 3.0 mm lens edge, so I had to scrape it out a bit with a knife point. Unless your printer is more accurate than mine, you might want to enlarge the slot a bit in the SCAD