This Freewell15mm Rail Mount Support for Eiger Matte Box supports and stabilizes your lens against sagging and vibration caused by its weight. It is commonly used with camera rigs or support poles. This rail support mount can be used directly in an Eiger matte box and also features a Y-shaped pulley for lens support; no limitation of zoom/focus in a constant position. Rotate the shaped nut to adjust the vertical height of the stand, suitable for various outer diameters.