Dog clutch

A dog clutch (also known a dog gears) is a type of clutch that couples two rotating shafts or other rotating components not by friction but by interference or clearance fit. 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.
Dog clutches are used where slip is undesirable and/or the clutch is not used to control torque. Without slippage, dog clutches are not affected by wear in the same way that friction clutches are.
Dog clutches are used inside manual automotive 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. Dog clutches are commonly used in racecars.
A good example of a simple dog clutch can be found in a Sturmey-Archer bicycle hub gear, where a sliding cross-shaped clutch is used to lock the driver assembly to different parts of the planetary geartrain.
In engineering, a "dog" is a tool or device used to lock two components in relation to each other.