?SOLID CONSTRUCTION: Made of metal, durable and solid; Metal construction for higher durability, assures years of corrosion and abrasion-resistant operaton ?DESIGNE: The Macro Focusing Rail Slider Plate Precision focusing through a 115mm adjustment range, With two Control knob can be convenient to Manual regulation, Helping to achieve exacting camera-to-subject distance ?FLEXIBILITY: The Rail is driven by a knob-controlled worm gear and index scales£¬which are printed on both sides of the rail in millimeters for consistency ?COMPATIBILITY: 48mm diameter metal thumbwheel with 1/4 inch Screw, Cameras can be mounted on top of the rail,The Base is a 38mm-wide Arca-type plate,with a 3/8 inch Bottom Screw Thread, You can attach it to your tripod,Ballhead ?Standard: Compatible with Arca-Swiss RRS Standard