Sunex SX264K, 1/4 Inch Drive Mini Right Angle Air Die Grinder Kit with Speed Regulator, Safety Throttle, Ball Bearing Construction, and Storage Case, 20000 RPM BUILT-IN SPEED REGULATOR: Regulated speed for better control. SAFETY THROTTLE LEVER: Maintain positive speed control. BALL BEARING CONSTRUCTION: Allows for a longer tool life. STORAGE CASE INCLUDED: Comes with a convenient, blow molded storage case. FREE SPEED: 20,000 RPM DRIVE SIZE: 1/4