Pillars are the vertical beams that support the roof and separate passenger compartment windows. A-pillar — First, or most forward, roof support pillar located on either side of the windshield. Also known as “windshield pillar” or “A-post” B-pillar — Center roof support that divides the front and rear doors on 4-door and wagon models. On2-door models, the B-pillar separates the door and rear quarter window/panel. On vans and wagons, the B-pillar is behind the front doors C-pillar — Rear roof supporting member on most vehicles. On CUVs/SUVs, this pillar separates the rear doors and quarter panel glass D-pillar — Vertical, or sometimes diagonal, roof support member at the extreme rear of the roof or greenhouse structure on mini vans, CUVs/SUVs and some sedan body styles.