My wife wanted some finials for the curtain rod in her office, but she didn't like any of the ones she saw on Thingiverse, and didn't want to wait for shipping.
These are based on a picture she showed me of some finials she liked on Amazon.
By default, these are sized to fit curtain rods with a outer diameter of 19.5mm.
The TPU insert should be printed out of a flexible material like TPU, it will ensure the part fits snugly on the rod without risk of falling off.
Keep in mind, depending on the design of your curtain rods, you may need to scale the insert to accommodate a smaller rod on one side.
Depending on your printer and how dialed in your settings are, you may need to print with support. I'd definitely recommend enabling z-hop with this print.