Despite the similarity in how scratches are generated, there are numerous styli referenced in test methods. Taber offers a number of these interchangeable tools, but cautions against comparing results obtained using different shaped styli. The shape of the stylus can impact the stress distribution as the stylus tip is moved across the material surface as well as the frictional drag.
Regardless of the styli shape, it is important to monitor the wear of stylus tips. Over time, tips may become blunt which increases the contact area of the tip and can reduce the cutting action making the tip less sensitive. Asymmetrical wear on the stylus tip may also occur which can increase the friction during scratching. And due to material differences in the test specimen, there is no way to predict how long the tool will last. If you have access to optical measurement equipment that offers an accuracies of ±0.01mm and ±1°, you can monitor the wear on your scratch tools. Inspect the tool at set intervals (e.g. every 250 or 500 tests), if any flatness or other kind of damage is found the scratching tool should be rejected and replaced with a new one.