This Manfrotto 823 Medium Hydrostatic Arm features an improved locking mechanism. A ball pivot encapsulated in a hydraulic oil-filled chamber enables the arm to be locked in position with only a gentle turn of the knob. This is accomplished by the fact that the oil surrounds the ball joint and applies pressure evenly, as opposed to a traditional lock that simply jams a screw or cup against the ball.
The 823 Medium Hydrostatic Arm spans 9.25" (23.5 cm) and is a perfect platform for a light fixture or camera under 8.8 lbs (4 kg) in weight. It also features both a 1/4"-20 threaded pin and a 5/8" pin to mate with a superclamp.