GM-51812 is used to align the automatic transmission range switch (inhibit switch) any time it is removed for service. To install the range switch, the switch is placed over the manual selector shaft, and the fasteners are loosely installed. GM-51812 is placed over the manual selector shaft and the switch, and the switch is moved until the pin on GM-51812 engages the hole in the transmission case. The switch fasteners can then be tightened to the specified torque.