I needed holders for hanging string lights in my roof vents and came up with this.
It is made for Cedral vents and can lock in place with a locking tap. It should fit other vents with the same spacing, but may not fit as tight.

Installation:

1. Slide into slot.
2. Twist a 90 degrees.
3. Pull down and wiggle a bit.

I printed in PTEG because I plan to leave them in place until needed again. The wall is facing south and gets really warm in the summer, so PLA is not suitable for in my case.