A ratchet is an orchestral musical instrument played by percussionists. Operating on the principle of the ratchet device, a gearwheel and a stiff board is mounted on a handle, which can be freely rotated. The handle is held and the whole mechanism is swung around, the momentum making the board click against the gearwheel, making a clicking and rattling noise. Alternatively, smaller ratchets are sometimes held still or mounted and the handle turned rapidly by the player.

One popular design has a thick wooden cog wheel attached to the handle and two wooden phlanges which alternately hit the teeth of the cog when the handle is turned.

It is similar to a football rattle , which is sometimes used in its place when a particularly loud sound is needed. An example of its use is Richard Strauss's piece Till Eulenspiegel's Merry Pranks .