Stand, sit, or kneel! The Rocker Board moves in one directional plane and has a large square design for beginners, The Wobble Boards move in multiple planes and have a smaller round design for intermediate and advanced users, Both Wobble Boards offer 3 levels of difficulty and adjust in seconds, All 3 boards feature birch wood construction with slip-resistant top, Wobble Board (16"" diam, ): 15, 17, or 20 degree angle, SKU: PWSS693