Perfect Fitness Ab Carver Roller for Core Workouts Ultra-wide ab roller wheel with built-in resistance to help maximize core workouts Interior kinetic carbon steel spring offers resistance on the roll out and assistance on the roll back to activate abdominals and arms Ultra-wide wheel tread offers stability for multidirectional exercises, and makes it easy to tailor workouts to be easy, medium or hard Ergonomic hand grips are angled to activate arm and core muscles; handles are removable for easy storage and transport Measures 9 x 18 x 8 inches, and weighs 4.6 pounds; one-year manufacturers warranty