Grinding or clicking noises from the drivetrain of your YIKONG YK4107 can be caused by worn, dry, or damaged bearings, including the Bearing 12x18x4 (21122). If cleaning and lubrication do not resolve the issue, replacing the bearing is recommended to protect other drivetrain components such as gears and shafts.
The YIKONG YK4107 Bearing 21122 has an inner diameter of 12mm, an outer diameter of 18mm, and a thickness of 4mm. It is made of metal and is listed as compatible with the YK4106/YK4106 Pro platform.