This Aluminum GT2 Timing Idler Pulley For 6mm Belt 20 Tooth 5mm Bore pulley works with GT2 6mm wide timing belt. This idler is a good match for 20T GT2 driving Timing Belt Pulley.
Idler pulleys are rollers that do not produce any mechanical advantage, nor transmit power to a shaft. They have a set of bearings pressed into the centre bore. The bearings allow the pulley to spin freely on a stationary shaft or bolt. They are used to lead a belt around a bend or to take up slack in a drive chain. They are also used to drive the belt on a non driven axle.
Many DIY 3D printer makers are using idler pulleys based on 3D Printed pulleys.
An inaccurate printed idler decreases printing quality and creates vibrations since the outside diameter of the idler is not concentric to the rotation axis. Other makers are using double bearings with stationary washers clamped from both sides. This is a better solution to improve belth driven assemblies performance.