Fixed Ring Gear:
6 for a set, hard engineering plastics, and film industry standards. The same outside diameter, inner diameter is respectively: 110 mm; 100 mm; 90 mm; 80 mm; 70 mm; 60 mm. By adjusting the screw, each increase 10mm.

Through the screw each can be adjusted adds 10 mm. Easy to install, can be used with the follow focus, when used alone, due to increased lens diameter, more convenient to use.