4 inch elbow

I've been working on improving the ventilation for my laser in my craft room. I originally started with this 4" duct to 5.1" window vent adapter from Printables. I liked the splines on the 4" side so I used that same pattern for the rest of my ducting. This model is a 4" elbow. See my other designs for the unions, fan mounts, and tubing extensions.