This CNC-machined K-20II Ball Head from Sirui is Arca-type compatible, and it includes a quick release plate with a threaded 1/4"-20 camera mount. Safety stops located on the bottom of the plate prevent it from sliding out if the clamp is partially opened. The head's load capacity is 55.1 lb, its weight is 14.1 oz, and it is 4.0" tall. The main aluminum locking knob disengages, and it allows you to move the ball and place it at a 90° angle; the independent pan knob also unlocks, so you can rotate the head a full 360°. Tension can be increased or decreased to the main ball with its control dial located on the inside of the main knob. The three spirit levels ensure that your horizon is straight at each axis.