Switchbot U Rail bearing extender

### The problem
The curtain rails I have in my home (Dutch, Kwantum brand) don't have the flat profile that many others have, they are more of a curved shape. This caused the u-rail Switchbot (U Rail v1) to sit off center, which in turn causes friction and damage to the rails. The damage causes slipping and drift when opening/closing the curtains.

### The solution
The solution is to print small o-rings that fit around the bearings making them fit in the slot better. Now it runs much smoother. See pics for more details.

Downside is that it is a but more difficult to fit the Switchbot back in the rails after fitting the bearing extender rings. But you wouldn't be looking for this part if this would deter you, right?