The Opteka FF220 Rail-Free Reversible Follow Focus helps you shoot videos with smooth, precise focus control. Whether shooting with a fixed-lens camcorder, video-capable DSLR, or other compatible camera, the precision-machined FF220 Follow Focus system provides repeatable, accurate focus pulling. It mounts directly to a camera, though it can attach to a standard 15mm rod system via the included adapter.
 
https://www.bhphotovideo.com/c/product/1195640-REG/opteka_ff220_rail_free_reversible_follow.html