BODY BOLSTER. The transverse members of the railcar underframe which is located over the
trucks and transmits the load carried by longitudinal sills to the trucks through the center plates.
BRAKE BEAM. The supporting structure for the two brake heads and two brake shoes acting
upon any given pair of wheels.
BRAKE CYLINDER. A steel cylinder attached to the body frame or truck frame of a railcar or
locomotive. It applies the brakes when supplied with air pressure. When the air pressure is
released, the piston is returned to its normal position by a release spring coiled about the piston
rod inside the cylinder.
BRAKE PIPE. That section of the air brake piping of a car or locomotive which acts as a supply
pipe for the reservoirs and is the means by which the car brakes are controlled by the engineman.
When a train is made up and all brake pipes on the cars are joined, the entire pipeline comprises
what is commonly called the "train line."
BRAKE ROD. Any of the rods which form the connections between brake levers and through
which the braking force is transmitted.
BRAKE SHOE. A block of friction material formed to fit the curved surface of the tread of a
wheel, and riveted or otherwise bonded to a steel backing plate having provision for quick and
positive securement to the brake head. Brakes on most conventional railroad cars depend on
friction created by the brake shoe rubbing on the wheel tread during a brake application. Brake
differing friction characteristics, cast iron and composition shoes are not interchangeable.
BRAKE VALVE. The valve in the locomotive with which the engineer operates the brakes.
The term is also used to refer to the control valve on a car.
BRIDGE TIE. A transverse timber member resting on the stringers of a bridge and supporting
BUFF FORCES. The force on a draw bar that compresses (pushes) on a draw bar. Buff forces
tend to push the train together.
BUFFER CAR. A railcar placed between the locomotive or an occupied railcar and a railcar
transporting hazardous material.
BULLPEN. A storage area for incoming and outgoing commercial railcars.
CAPACITY. The nominal load in pounds or gallons that a railcar permitted to carry. These
figures are stenciled on the car and are identified as "CAPY." Capacity is not to be confused with
load limit, which is the maximum weight that can be loaded in a given car.
CENTER PLATE. A cast or forged steel plate riveted or welded to the body bolster and the
truck bolster at the railcar centerline, the function of which is to transfer the body bolster load to
the trucks through the truck bolster.