The Brompton Chain Tensioner Assembly is a genuine Brompton spare part.The Brompton chain tensioner is one of the "essential" list of spare parts for Bromptons with a single rear sprochet and performs an important role in keeping the chain taut whether the bike is being ridden or in the folded/parked position. This chain tensioner is for internally geared hubs where only one single rear cog / sprocket is fitted (1-speed, 3-speed or the older 5-speed).