Sturmey-Archer was a manufacturing company originally from Nottingham, England. It primarily produced bicycle hub gears, brakes and a great many other sundry bicycle components, most prominently during its heyday as a subsidiary of the Raleigh Bicycle Company. In the past, it also manufactured motorcycle hubs, gearboxes and engines.
A Sturmey-Archer three speed hub, the most common kind of Sturmey-Archer gear
An exploded Sturmey-Archer AW
The internals of a Sturmey-Archer FM four-speed, medium ratio, hub gear. It has substantially more components than an AW 3 speed. FC, AF, AC, and ASC hubs are similar.
Sturmey-Archer X-FD front hub brake
A hub gear, internal-gear hub, internally geared hub or just gear hub is a gear ratio changing system commonly used on bicycles that is implemented with planetary or epicyclic gears. The gears and lubricants are sealed within the shell of the hub gear, in contrast with derailleur gears where the gears and mechanism are exposed to the elements. Changing the gear ratio was traditionally accomplished by a shift lever connected to the hub with a Bowden cable, and twist-grip style shifters have become common.
Sturmey-Archer S3X
early NuVinci hub
NuVinci internals
A Sturmey-Archer AM bicycle hub gear mechanism with the ring gear removed to show the compound (stepped) planet gears.