The modular ARRI FF-5 Cine Basic Follow Focus Set consists of a single-sided follow focus with one standard knob. This unit snaps onto a pair of 19 or 15mm lightweight support rods. The FF-5 Cine combo is designed with a 2:1 knob-to-gear ratio for smooth, accurate focus pulls on cine-style lenses. Two focus gears are included with this unit, one for primes and smaller zooms, and one for larger primes and 35mm zoom lenses.
The FF-5 Cine Set features a modular design that is compatible with an array ARRI follow focus accessories such as whips, speed cranks, and knob accessories. One flat marking disk is included with the FF-5 Cine Basic Set. The FF-5 Cine unit may be used with an adapter on 19/15mm studio rods.
https://www.bhphotovideo.com/c/product/1288926-REG/arri_kk_0005757_follow_focus_ff_5_cine.html