Air duct clamp. Was sized to model: https://www.printables.com/model/285440-duct-flange by thinkingalaud. Should fit other standard air ducts.
Additional parts:
2x M5 nuts
2x M5-16 or longer screw
I printed in PLA and have been using it for several weeks. I have not noticed any damages, so PLA should hold fine. Tolerance for the nut is a little tight, so print accordingly.
The author marked this model as their own original creation.