KMC

Founded in 1977, KMC just makes chains. They don't need to diversify because the chains they make are very good. Not so much aftermarket as an upgrade, KMC's BMX chains are about as tough as you're going to get, and their road chains are cheaper, smoother and lighter than a lot of the main manufacturers. With their focus solely on chains, KMC do a prodigious amount of R&D to make real improvements over the competition.