The old plastic parts under our chairs not only did melt with gaining age, but also made nasty traces on our floor. Replacing them was a quick print, easy installation and really satisfying. 

The “nipple” parts is 6mm wide to fit our chair's holes. The base part is 10mm in diameter and should be enhanced with a felt disc, which can be found in your local shops or online. This adds comfort and noise reduction.
If you need other dimensions, feel free to file me a comment here.

Printed in PETG for robustness. Feel free to try a PLA, but might be too brittle to sit on.