U-Groove Ball Bearing - U604ZZ - 4x13x4mm

Roller bearings use rolling elements, in this case balls, to reduce rotational friction and support rotational and axial loads. The load is transmitted through the balls from an outer to an inner race and due to the fact that the balls are rotating, there is a much lower coefficient of friction compared to two surfaces sliding over each other. In most cases one of the races is stationary, while the other is attached to a rotating assembly.

This U-Groove ball bearing is commonly used in 3D printers where it functions as the filament idler bearing in extruder assemblies. Filament is sandwiched between this bearing and a hobbed drive gear, which bites into and drives the filament down into the hotend. The groove restricts the feed path channel and reduces the chance of filament buckling out the side during a print. This U604ZZ bearing is sealed on both sides to protect against dust and dirt.