On-One Doofer Singlespeed Chain Tensioner
Got a geared bike that you want to run as a singlespeed? Decided your commuting bike needs the fuss-free reliability of hub gears? The On-One Doofer chain tensioner takes up the slack with a simple sprung arm and jockey wheel.
Screws into the gear hanger. Adjustable side-to-side for chain position.
