Was watching a YouTube video of a chap tearing down the Niche zero to see how well it was built - materials, tolerances etc which by the way showed it as excellent for a consumer unit - and saw that when he took the base cover off showing where the excess cord is stored, hidden there are two spare springs that the outer burr sits on.
I am not sure if I would know when they would need replacing, but I guess they might at some time. Interestingly, I could not find any mention of them being there in the user manual.