Geared steam locomotive
A geared steam locomotive is a type of steam locomotive which uses gearing, usually reduction gearing, in the drivetrain, as opposed to the common directly driven design.
Stephenson valve gear
Stephenson valve gear is a convenient arrangement for any engine that needs to reverse and was widely applied to railway locomotives, traction engines, steam car engines and to stationary engines that needed to reverse, such as rolling-mill engines. It was used on the overwhelming majority of marine engines. The Great Western Railway used Stephenson gear on most of its locomotives, although the later four-cylinder engines used inside Walschaerts gear.