Hands down, one of the best cogs in existence. Perfectly round. Perfectly threaded. Perfect tooth profiles. They are coated with titanium nitride for optimal lubricity and durability so this cog is a top choice among pro racers. These are 1/8" thick for use with track chains, such as those from HKK, Izumi, and DID. They are a good match for Sugino 75, Zen chainrings, and Dura Ace NJS chainrings. These cogs come with their own nice color matched canvas/leather carrying pouch, which you can use to store the cog safely.