CrMo steel, heat treated (hardened and double tempered) sprocket / cog for converting bikes with Shimano HG 7-/8-/9-/10-speed and compatible cassette hubs to a single speed bike, with wide foot to avoid digging into alloy splined HG type freehub bodies, available with 12. 13. 14. 15. 16. 17 or 18 teeth.