Woodruff keys, also known as "half-moon keys", are another type of key and they are used to improve the concentricity of the shaft and the mating part which is critical for fast moving operations.
Woodruff keys, also known as "half-moon keys", are semicircular shaped keys that, when installed, leave a protruding tab. They are used to improve the concentricity of the shaft and the mating part which is critical for fast moving operations.