This is the 2 ball bearing installed compatible level winder worm shaft of ABU 2500C, made by aluminum alloy to remove weight. This new version has a screw fastening the gear to the shaft, and you may change the ball bearing on the shaft. Fits to 2500C, 2501C, 2600C, 2601C, 3500C with a metal cup washer at level winder. Doesn't fit to the oldest model without it. 4.4g (genuine worm shaft 6.1g) Ball bearings removes friction in roration drastically. Plastic part is made of Duracon POM to offer friction-less operation.