The posts in a vehicle are the almost vertical structural pillars that support the window, door and roof area of a car and connect the roof of the vehicle with the base of the frame. These supporting posts are labelled A post, B post and C post. In larger cars there is also a D Post.
Usually steel or alumnium, the posts in a car are solid structures, which are welded at one end to the car's frame and at the other to the roof panel and are positioned between the windows or doors. The B post is the pillar in the centre of the car, supporting the roof panel and the doors. The B posts also function as a place to latch the front doors and where the hinges on the back door are mounted. The specific design of the B post will vary depending on the design of the car. The B post on the car interior is usually upholstered with cloth, leather or suede to match the rest of the car's interior design.
Supporting the vehicle's roof and door, the B post plays an important role structurally in the overall safety of the car and its occupants. The B posts have a vital role to play in a collision by adding structure to and protecting the passenger area of the car, preventing it from crumpling, while absorbing some of the impact of a side collision.
Usual reasons for B post replacement is due to damage received in an accident. Buying a new B post will give you a part that's compatible with the make and model of your vehicle, ensuring this important structural body part can perform properly.