Keep your blood flowing by maintaining balance during active sitting with the Merrithew™ Stability Ball Base, which activates core muscles and helps to reduce back pain by stabilizing the spine. Tighten Core Muscles Stabilizes your exercise ball during workouts or turns your ball into a chair Increases blood flow during active sitting, which helps keep the mind sharp and focused Helps to activate core muscles while stabilizing the spine to reduce back pain Key Specs Diameter: 18.9’’ Height: 3’’ Additional Details Fits any ball 18’’ wide or larger