Brompton
13T rear sprocket 3.1mm for BWR 6 speed, 3/32" chain, Shimano splines.
This sprocket is used as standard on the Sturmey Archer BWR (Brompton
Wide Ratio) six speed rear wheel It can also be used on the single / two
speed Brompton rear wheel (though as standard the single speed uses a
12T sprocket and the two speed uses a 12T / 16T combination)