Fig. 1922.
In [Fig. 1922] are segments of two wheels, a and b (corresponding to a and b in [Fig. 1921]), but with their teeth arranged for a Brown and Sharpe milling machine, in which the machine spindle has a left-hand thread; hence the direction of cutter revolution is reversed, as denoted by the arrows in the two figures.
Fig. 1923.
Fig. 1924.