If it's not a screw on 'block' as I call them, it may be an old ug cassette where the smallest sprocket threads onto the freehub. The usual way to remove is with two chainwhips.Hi there, hope I've got this right, I want to upgrade my Raleigh Mirage, but am having trouble removing the rear cassette, it does not appear to be like any other I've seen. Any advice please.