CowboyStudio Follow Focus Finder F0 With Gear Belt and Quick Release Clamp for 15mm Rod Support DSLR One (1) Follow Focus, One (1) Matching Gear Belt Fit Rail Distance : 60mm/2.4", Fit Rail Diameter : 15mm/0.59" Dial Index Adjustment : 360 degrees Gear MOD: Industry standard 0.8, Gear Belt Fits Lens : 52 mm to 86 mm Max Length: Approx. 235mm/9.25", Adjustable height: Approx. Between 1-4cm / 0.39-1.57"