This is the Sturmey Archer S-RF5(W) hub with the N version driver (9-spline driver). Two sprockets can be fitted on this driver, turning this hub into a 10 speed.
Sturmey Archer S-RF5(W) is different from the 5 speed sprinter hub equipped on earlier Bromptons. Unlike the sprinter hub which has the same overall range as the S-RF3 3 speed hub, this wide ratio version has a much wider range of 256%. Brompton BWR 3 speed hub has a range of 245% in comparison.
This kit is well suited for converting your 2- or 6-speed Brompton into a 5x2, or a 10 speed. This kit does not include the two speed shifter, derailleur, tensioner, and the related fittings. If you have a 2- or 6-speed, you already have this eqiupment. If not, you can get the derailleur upgrade kit from Brompton dealers.
We have assembled the gearing ratios for various combinations of sprokets and chainrings here, which may help you select the right sprocket.
It is well known that Sturmy Archer S-RF5(W) gear hub is not the easiest to adjust, due the small window for proper adjustment. This was also compounded by the fact that Sturmey Archer instructions do not apply to Brompton. In our package, we will include an adapted instruction for Brompton, but it will still require a good patience for initial adjustment.