Helinox Vibram Ball Feet SetThe Vibram Ball Feet Set from Helinox is designed to keep your chair rock solid on uneven ground The 45mm set is compatible with the Chair One, Chair One Mini, Chair Two, Chair Zero, Chair One Large and Cot Extension Legs. The 55mm set is compatible with the Chair One (re), Chair One High Back (re), Swivel Chair, Chair One XL, Sunset Chair, Savanna Chair, and Bench one.