Truck bolster

A bogie or railroad truck holds the wheel sets of a rail vehicle.

Also called an axle box, or journal box in North America, an axlebox is the truck or bogie assembly that houses the end of the axle. Early axleboxes contained friction bearings in which the axle spun in a bed of oil. Friction bearings are now illegal in interchange service in the United States; modern axleboxes use roller bearings. As early as 1908 they contained a set of long cylindrical rollers allowing the axle to rotate. It was also used on steam locomotives such as the Victorian Railways A2 class, the LMS Garratt, the LSWR 415 class, and the GCR Class 1.

A large steel pin—or rod—which passes through the center plates on the body bolster and truck bolster. The truck turns about the bolt, and stress is taken by the center plates.

One of a pair of plates which fit one into the other and support the car body on the trucks allowing them to turn freely under the car. The one on the truck may also be called center bowl.

The frame at either side of the truck.

Each truck has a bolster—a transverse floating beam—between the side frames. It is the central part of every truck on which the underframe of the railcar or railroad car is pivoted through the center pivot pin.

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Wikipedia