For experienced jugglers. It's easier to give a spin and maintain it! Longer lifespan of the string. What is special about a diabolo with a one-sided bearing? The bearing axis locks in one direction but spins freely in the opposite direction. A fixed axis cannot rotate by itself, so the friction of the axis against the string causes the diabolo to lose momentum when you stop accelerating it. With a bearing axis, the cups of the diabolo continue to spin even when the axis is not rotating, resulting in less friction on the string and less speed loss. This means there is less friction on the string and less loss of momentum, allowing for longer playtime. For example, you can hold the axis in a loop of the string without losing momentum. What should you really know? The axis has a black and a white part. For right-handed users, the black part should be closer to you; for left-handed users, it should be further away. Technical specifications: - Diabolo with bearings - Diameter: 10.5 cm - Length: 12 cm - Weight: +/- 120 g - Aluminum axle and rubber grip.