Fit all balance disc
Fitball Balance Disc 14" Diameter
Quick delivery, quality product -- can get cheaper balance disc but they are not as good. + Adjustable, -- inflates and deflates Slow.
I 've used it with a 17"x 22" plywood on top as a trainer for paddle boarding. After using a rocker board, the balance disc is more challenging. That's why I needed a quality cushion.