Pressure + Vibration A great multi-tool for getting warm. Sized between a baseball and softball the added vibration improves the effectiveness. Specifications Measurement: 3.75inch in Diameter Net weight: 0.66 lb AC adapter: Input 110V~240V 50/60Hz. Output 9V 1A. Lithium-ion Battery (Built-in): 7.4V 1200mAh