The author remixed this model.
The original roller did not grip 0.25mm soldering wire. This version has the roller's outer diameter increased by 6% while the inner diameter and thickness remain unchanged.
This way it can grip 0.25mm wire gently to push it through. Too much force and it will deform. Be careful how tight you screw the knob.
During installation I recommend removing the rollers so you can guide the thin wire easier.