JUYO VONSAN ab roller Ball bearings ab roller wheel with Knee Pad Abdominal Exercise Toning Wheel Double wheel Smooth Workout Double wheel with ball Bearings for smooth functionality and balance with Knee Pad ideal for abs, core and upper body development Comfortable to use with foam hand grips and knee pad This ab wheel roller is suitable for all skill and fitness levels, beginners to advanced the diameter of the AB wheel:14.5CM/5.7inch