Neewer A-B Stop Follow Focus with Quick Release and Gear Ring Belt Mount for DSLR Cameras Camcorder,Fits Shoulder Supports,Stabilizers,Movie Rigs,All 15mm Rod Mounts This A/B Hard stop enables precision focus adjustment,follow focus with quick release make mounting easily and quickly Grooved knob for slip-free control,A white marking disk can mark the focus point It allows mounted by both left and right side only if it is convenient for you Use gear drive to adjust camera focus in a more accurate and smooth way. Fits standard 15mm/0.59" rod mounts tightly.(60mm for center to center distance) An adjustable gear ring belt is designed to fit less than 100mm lense diameters