When the Top Tjet racers in the country build their cars, they Indicate In the Top gear to Zero Runout. (Wobble)
The bottom Pinion Gear wears over time and they need to replace the Pinion Gear without disturbing the Top Gear that they Indicated. 
The TGT-2 Tool - Removes the Drive Pinion Gear, WITHOUT DISTURBING the 24 Tooth top Gear
Now Nickel Plated