Arca-type Ball HeadThe compact professional SLIK PBH-635AC is an Arca-type compatible ball head designed for photographers on the go.The 635AC features a slim profile weighs 1.07 lbs 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 knob away from the head and rotate it to the desired position.The head includes a single U-notch for greater flexibility of camera position. You can point the camera straight up or down and shoot horizontal and vertical frames.The 635AC has a load capacity of 13.2 lbs and is capable of supporting full-sized professional cameras and