Shimano Cassette SpacersFor use on 11-Speed freehub body with 9 or 10-Speed cassetteUsing 10-Speed cassette on 11-Speed freehub body requires both 1.85mm (FW8991) and 1.0mm (FW4671) spacerUsing 9-Speed cassette on 11-Speed freehub body only requires 1.85mm (FW8991) spacer