E.3.5.1. high-speed-drive for Brompton folding bike
A very popular combination is the Brompton folder combined with high-speed-drive. It needs a +6.5 mm cone ring to allow folding (the rear chainstay folds where normally the gear housing is located) and a wider nut on the left side to make up for the additional width.
A good set-up is the standard high-speed-drive with its 27 t. chainring and integrated trouser guard. With such a chainring, you have much lower gears for climbing (27 instead of 50 t.) but also much higher gears for speed (67 instead of 50 t.).