The Shimano SM-GEAR cogs can be used for 3- to 11-speed Nexus and Alfine hubs. They are made of steel and are 2.3mm thick. The cogs are available in a 16-23 tooth version, and most of the time in black or silver.
Need help?
The technicians at your Decathlon store workshop are available to help you replace your bike's parts. Feel free to ask them for help!