The feet on my Helinox chairs had perished, and rather than replace them with standard skinny versions and adding a ball foot adapter, I made these replacements to enjoy the best of both worlds.  

The Helinox ball foot adapter accessory is 45mm in diameter and designed as a shoe to go over the standard foot to increase the footprint of the chair in soft conditions.  

These should fit Helinox Ultra Lightweight Chair models: Chair One, Chair Two, Chair One Mini, Chair Zero or  Chair One L.

These are 40mm diameter so that the chair still folds into the standard bag, and replace the standard feet, so be aware that they won't fit the rocking feet or ground sheet accessories should that be a consideration.

Mine are printed in Flexfill 98A in 0.15 layers with 25% infill, with a 4mm brim on the inside only, which helps stability as the print progresses.

Print upright as shown without supports.