Neewer A-B Stop Follow Focus C2 with Gear Ring Belt for DSLR Cameras Such as Nikon,Canon,Sony DV/Camcorder/Film/Video Cameras,Fits 15mm Rod Mounts,Shoulder Supports Completely gear-driven design for slip-free, accurate, and repeatable focus movement This Follow Focus Integrated with A/B Hard Stops which have easy begin/end setups for fast repeatable racking between two points, and make focusing lenses that have no hard stops (such as Canon EF lenses) much easier. Mounts onto 15 mm Rod Support (60mm center to center difference). Gear drive can be mounted from both sides The white mark ring is made of magnet material. It can be detached or attached very easily and quickly on metal-made follow focus.