What do automatic transmissions, electric screwdrivers and corkscrews have in common? They all use planetary gears: the "sun" or the center gear engages all three "planet" gears or outside gears for maximum efficiency. Planetary gears are ideal where ruggedness and high torque are needed. Opening a corked bottle can really be a chore. With the 6:1 gear ratio in the Planetary Corkscrew, removing the cork is easy.