The Twenty6 Products Cog expands the gear range on your 10 speed drivetrain, and adds some bling in the process. As you've come to expect from the crew in Bozeman, it's impeccably machined out of hard wearing 7075 aluminum plate, for a long service life. And that's to say nothing of the bevy of stunning anodized color options.In essence, adding a larger cog to the inside of your cassette gives you one lower gear, which can be the difference between cleaning that hairy climb, and being thwarted yet again an especially important consideration on today's one by drivetrains. To make room for this cog, you'll have to remove an individual cog from your cassette. The most common one to pull is the 15t cog typically found on modern mountain cassettes. This can leave a large gap in your spacing, however, which is why many riders have taken to replacing the 15 and 17t cogs with a 16, which provides a smaller jump and smoother shifting. The Twenty6 Products Cog is available in two sizes, from 40t, to 42t, and in the colors Black, Blue, Gold, Green, Mango, Pink, Purple, Red, and Yellow.