Unfortunately the manufacturer cannot disclose with us the diameter size or if the 5/8' will fix. You are welcome to call the manufacturer Chapin, 1-800-950-4458, for further assistance on this matter.Â
The inside hole of the gearbox that the axle would go through has a diameter around .625 inches.
Unfortunately since the Chapin 82080 Spreader was discontinued, the gearbox and parts for that unit were discontinued as well. We contacted Chapin and they stated they do not have any other gearboxes that are compatible with that model.