Coarse focus (A) is via a rack & pinion. Fine focus (B) is via a fine thread/spring system.
Coarse focus pinion gear. The embossed "2" may have been the coarse mechanism model.
Coarse focus threaded rack attached to the microscope body tube.
Fine focus control knob.
The microscope body is attached to a sleeve. The sleeve moves when the fine focus knob is turned.