I lost one of the rubber feet for my REI camp chair when a leg sank into soft ground. I looked forever trying to find a replacement, but nothing fit. I first designed a suitable replica of the original, and it worked as expected. But then I decided to improve on the design to keep the leg from sinking in wet or sandy soil. It works great. . . much better than the original. I've added both files, so you can print whichever suits you the best. My chair leg measures ½" in diameter (12.7 mm), so if your chair is the same, it should work for you.
I printed them using TPU filament, which makes them extremely tough, as well as giving it some grip. I also printed with 100% infill, again for strength.
The author marked this model as their own original creation.