If you've got a single-speed cassette body on your rear wheel, you can use just about any splined cassette on the market. We have to admit that we're partial to the Chris King Stainless Steel cog. It's heat-treated and then bead blasted for great strength and looks. Looks good, rides great, lasts forever, and gives a little Chris King style to any single-speeder.
The Chris King Stainless Steel cog is a single splined cog. It is designed for use with single-speed cassette hubs. It is not supplied with a lock ring. Cogs available run from 17-20 teeth. The color is Silver. Claimed weight on the 17-tooth cog is 31g, on the 20t 52g.