A dog clutch (also known as a dog ring, clutch dog, dog gear, or positive clutch) is a type of clutch that couples two rotating shafts or other rotating components by engagement of interlocking teeth or dogs rather than by friction. The two parts of the clutch are designed such that one will push the other, causing both to rotate at the same speed and will never slip. In engineering, a "dog" is a tool or device used to lock two components in relation to each other.
Dog clutches are used inside constant-mesh manual transmissions to lock different gears to the rotating input and output shafts. A synchromesh arrangement ensures smooth engagement by matching the shaft speeds before the dog clutch is allowed to engage. Racecar, motorcycle, and large truck transmissions, having higher performance demands and less need for smooth engagement than passenger cars, commonly employ dog clutches unsynchronized to engage gears due to their high strength and durability and low complexity and weight. These unsynchronized gearboxes are nicknamed dog boxes and allow clutchless shifting.