Arca-type Ball HeadThe compact professional Slik PBH-535AC is an Arca-type compatible ball head designed for photographers on the go.The 535AC features a slim profile weighs 13.4 ounces includes a universal Arca-type quick release platform so you can use just about any Arca style quick release plate L-bracket and is even compatible with backpack Clip design plates.It includes 3 control knobs to control the functions of the head.Large Lock/Release Knob to control framingTension knob to control the friction of the ball movementPan Knob controls 360?. panning left and right independent of the ball movementThe lock release knob is also spring-loaded. Simply pull the lock knob away from the head and rotate it to your preferred placement.The head includes a single U-notch for greater flexibility of camera position.