The transmission driving ring (red) has to be placed on an axle joiner (Blue). This makes the transmission driving ring rotate together with the joiner; at the same time, the ring can slide forward or backward along the joiner. Figure 17-4 shows what happens when we put two 17-tooth gears eith clutches on the axle next to the ring. The gears rotate freely on the axle. unless engaged by the driving ring that slides into them.
The easiest way to control the transmission driving ring is to use another special piece called the transmission changeover catch, shown in Figure 17-5 it was developed specifically to move the ring back and forth, engaging and above the ring, on a separate transverse axle