What is the name of the gear that allows two gears to rotate in the same direction?

The correct name for the gear that allows two gears to rotate in the same direction is the idler gear. This type of gear is positioned between two other gears, which can be rotating in opposite directions. The idler gear's primary function is to maintain the direction of rotation of the driven gear while allowing the driving gear to maintain its own direction.

When the driving gear turns, it causes the idler gear to rotate in the opposite direction. Consequently, this idler gear then drives the second gear, resulting in that gear rotating in the same direction as the driving gear. This mechanism is particularly useful in various applications where maintaining orientation is crucial without altering the speed or torque.

Other terms like coupling gear, follower gear, and driving gear refer to different functions or positions in gear arrangements and do not specifically describe the role of allowing two gears to spin in the same direction as effectively as the idler gear does.