This is a modified hub for the QuattroBox that replaces the original integrated pressure arm with a more robust, spring-loaded mechanism.
In the stock design, the bearing that presses the filament against the encoder gear is supported by a small plastic arm molded into the hub housing. Over time, that arm can wear, deform, or lose consistent pressure.

In this modification, the pressure arm becomes an independent printed lever mounted on a screw that acts as a hinge pin. The filament-tracking bearing is installed on this lever, and a compression spring (4.0–4.5 mm diameter, ~10 mm length) provides consistent tension against the encoder gear.
The result is smoother filament movement, more reliable encoder readings, easier maintenance, and significantly improved durability.

All parts are easy to print, and the mod fits directly into the existing QuattroBox layout. No changes are required in firmware or software.
 

Materials:

• Compression spring: 4.0–4.5 mm outer diameter, approx. 10 mm length
• M3x12 mm Allen screw, used as the hinge pin for the new lever arm
• M5 screw (4 mm length), used to close the access opening where the spring is inserted
  (you may cut down a longer screw if needed)
• Thin M3 washer, placed between the lever arm and the hub body to prevent plastic-to-plastic friction
• 2x M2x10 self-tapping screws to secure the switch
  
  
  PS:. The part is already pre-supported; remove the supports (both the original one and the one in place of the arm).