The coarse focus is a rack and pinion mechanism located within the tube of the supported upright.
Fine focus consists of a threaded thumb wheel (arrow) that presses against a beam. The beam, in turn, pivots within the body tube and moves an internal spring-loaded sleeve. The objective holder is threaded onto this sleeve. Turning thumbscrew B moves the objective up or down relative to the specimen. A standard thread pitch for microscopes of this vintage is 300 threads per inch.