Variations on a 4" box fan adapter to round, 4"-ish exhaust or vent pipe, spouts, and flangesI have a Full Spectrum laser cutter and had a monster 2HP dust collector for exhaust, but the dust collector was so loud I could hardly hear anything when it was running. The specs for the laser cutter said the exhaust needed to be 60-100CFM and I had two box fans that were each 140CFM so decided to replace the loud dust collector with two 4" box fans. The problem was putting a fan inline with a 4" outlet of the laser and 4" pipe and exhaust vent to the exterior.So, I made some adapters that bolt onto either side of the fan and are various sizes of inner and outer diameter to fit various situations around 4" pipe. I added one box fan directly in front of the exterior exhaust vent tube and one directly out of the laser cutter. The two working together move plenty of air to suck out laser cutting vapors and smoke. The beauty is it's much quieter than the 2HP dust collector.The fan mounting holes are sized for #6-32 but M5 bolts will thread into the holes nicely, too.The following STL files have various inner and outer diameters and slightly different shapes. #1 has set screw holes already positioned on the flange.-1.stl has an inner diameter of 4", outer diameter of 4.4" and is good for go over a 4" OD flange such as on the Full Spectrum laser cutter -2.stl has inner diameter of 4.2" and outer diameter of 4.4" -3.stl has inner diameter of 3.792" and outer diameter of 4.2" -4.stl has inner diameter of 4" and outer diameter of 4.4" - the tube is longer than the -1.stl but otherwise similar shape and size.With these four sizes it's quite easy to bolt on the adapters you need for various 4" vent pipe problems.