Gearboxes are found in Sorrow's Furnace, where they are used as locking mechanism for doors. To open a door, a player has to activate a gearbox next to it by placing a master gear in it. Master gears can be retrieved from any other active gear box. When a master gear is taken from a gear box it will become inactive (i.e. you can take only one master gear from a gear box), but it can be reactivated by placing another master gear in it. Active gear boxes can be recognized by their moving gears and orange light coming from the lower part, while inactive gearboxes will be motionless and dull.