Simple 3 to 4inch dryer duct adapter. I designed it for use with one of those Chinese diesel heaters often used for camping/overlanding. Mine was printed from nylon for higher heat resistance and to play around with using string trimmer line. Should work fine in PLA or PETG if not used in a high-heat application. Printed entirely with walls for strength. 0.2mm layer height. Used the stock Bambu Lab nylon profile.