Since the Knoop indentation is rather long and narrow and less deep compared with broader and "rounder" Vickers indentations, the Knoop method is primarily suitable for testing very thin layers (e.g. aluminium foil) as well as hard and brittle materials, such as glass and ceramics. The deeper Vickers indentation can cause cracks around the edges of the test indent in these materials, which can be avoided with the shallower Knoop indentation.
From a geographical perspective, the Knoop method is used above all in the USA, while it is less common in Europe.
The following table shows the standardised Knoop methods (test loads between 10 gf and 2 kgf) together with the associated test forces and applications.