Sette Single Speed Tensioner
Convert your vertical drop-out bicycle to a single speed. The Sette single-speed chain tensioner will adjust the tension to keep you and your chain moving along smoothly for miles and miles. It has an easily adjustable in-and-out bolt for proper chain line and mounts on the rear dropout. It's also super light.
I've had this on my 90's Specialized Rock Hopper Single Speed conversion for 2 years now. At my recent wheel true up session, the mechanic commented that he thought it had better tension than 2 or 3 others he had tried. The adjustability made the hard part of the conversion (lining up the chain) pretty easy for me. My bike sits outside year round in Chicago, and after two years, this piece still looks great.