Black Gear

Black Gears (黒い歯車) are evil devices used by Devimon to control good Digimon and turn them evil. The Digimon under their influence can be set free by destroying the gear or by a DigiDestined's Digivice, which expels evil. Black Gears are used to tear File Island apart, and messing with them also brings the pieces back together. These are only featured in Digimon Adventure, but the theme is revisited in Digimon Adventure 02 via Dark Rings, Dark Spirals, and Dark Spores as well as the Black Digi-Core in Digimon Next.

Instances of Use

 * Meramon is the first known Digimon to be controlled by a Black Gear at Mount Mihirashi near the Yokomon Village. It is destroyed when Biyomon first digivolves to Birdramon and fights him.
 * When the DigiDestined activate the machinery at Factorial Town, a Black Gear slips into Andromon's exposed leg and controls him. It is destroyed by Kabuterimon's Electro Shocker in his debut appearance.
 * The Black Gear in Monzaemon causes him to turn the tables against kids by making the kids in Toy Town act as the toys for toys. Togemon takes care of it when she first appears.
 * On their trek up Infinity Mountain, Joe Kido and Gomamon are attacked by an Unimon controlled with a Black Gear. Joe attempts to remove it himself, but Gomamon saves the day as Ikkakumon.
 * Both Frigimon, who is rescued by Agumon, and Mojyamon, fought by Frigimon, Greymon, and Garurumon, are controlled by Black Gears on the Freezeland portions of the broken File Island.
 * When Devimon breaks apart File Island to separate the DigiDestined, the children are able to piece the island back together by damaging the Black Gears within it.
 * Centarumon is under the influence of a Black Gear in the Great Canyon, and it takes both Togemon and Kabuterimon to free him.
 * Leomon is infected by Devimon with the Touch of Evil, but is freed by Tai's Digivice, but is later reinfected. He is later powered by Black Gears which turn him into a larger, darkened version of himself. By using the light of their Digivices, Taichi "Tai" Kamiya and Yamato "Matt" Ishida manage to return Leomon to normal by driving out the Black Gears.
 * By drawing a large amount of Black Gears into his body, Devimon grows to a massive size and strength, defeating most of the DigiDestined's Digimon in the resulting battle. It takes Angemon absorbing the light from the Digivices as well as sacrificing himself in order to defeat him.
 * Though Devimon by this point has been destroyed, Black Gears continue to live on in Digimon that were already under their influence. Whamon and Drimogemon are both under the influence of the Gears, but are both freed by the DigiDestined. Drimogemon is of particular interest as Devimon used him to guard the DigiDestined's Tags, possibly preparing for the event of his death. Whamon is freed when the Black Gear in his stomach is destroyed by Tai with his Digivice and Drimogemon is freed when Kabuterimon destroys the Gear in him.

Trivia
The Black Gears are the subject of several cards: Bo-103: Kuroi Haguruma and Bo-104: Black Gears.