Each Xone mixer has specific sized inserts in the fader knobs’ cavity, marked A, B, or C. This is to offer the best fit in accordance with the different fader stem dimensions between the channel and crossfader. Please refer to this document to ensure that the correct knobs are fitted to the right faders.
Please use the image & table below to identify the insert type and part number when ordering spares. Spares can be procured through the A&H global distribution network,
https://www.allen-heath.com/where-to-buy/