A simple birdcage finial I made for our curtain rods. The rods are 3/4" aluminum conduit, and the finial slips on the outside. My printer only has 0.4mm tolerance, so they're slightly loose (better than too tight), but I put a dab of poster tack inside each one and they hold in well.
I printed them with 100% infill because they're so thin, but that might not be necessary as they're not structural or anything. I used tree structures and a small pliers to pull the trees out of the middle.
Spray painted with Rustoleum "Aluminum".