smokebox are: BlowerVertical pipe below the chimney petticoat pipe, with holes to blow steam upwards. Provides a draught to maintain adequate combustion – and to prevent smoke and flames from entering the cab through the firebox door – when the blastpipe is insufficiently effective, for example when a locomotive is stationary or the throttle/regulator is closed such as when coasting into a station; also helps to draw the fire when lighting up. Petticoat pipe / Apron Vertical pipe with a bellmouth-shaped lower end extending down from the smokestack into the smokebox; enhances and equalizes draft through the boiler tubes. Steam pipeCarries steam to the cylinders. Smokebox doorHinged circular door to allow service access to the smoke box to fix air leaks and remove cinders. Trailing truck Rear bogie Wheels at the rear of the locomotive to help support the rear of the locomotive and improve riding qualities – see also Leading wheel (46). Foot board / Run board / Running board / Tread plateWalkway around the locomotive, from the cab front, to facilitate inspection and maintenance. FrameThe strong, rigid structure that carries the boiler, cab and engine unit; supported on driving wheels (43) and leading and trailing trucks (14, 46). The axles run in slots in the frames. Early American locomotives had bar frames, made from steel bar; in the 20th century they usually had cast steel frames or, in the final decades of steam locomotive design, a cast steel locomotive bed – a one-piece steel casting for the entire locomotive frame, cylinders, valve chests, steam pipes, and smokebox saddle, all as a single component. British locomotives usually had plate frames made from steel plate but some end-of-era designs included cast steel sub-frames. Brake shoe / Brake blockCast iron or composite material that rubs on all the driving wheel treads for braking. Sand pipeDeposits sand directly in front of the driving wheels to aid traction on steep gradients, when starting or when the rail surface is not dry and clean. Coupling rods / Side rodsConnect the driving wheels (43) together. Valve gear Motion System of rods and linkages synchronising the valves with the pistons and controls the running direction and power of the locomotive. Connecting rod / Main rodSteel arm that converts the reciprocating motion of the piston into a rotary motion of the driving wheels. The connection between piston and main rod is a crosshead, which slides on a