GM A platform

The General Motors A platform (commonly called A-body) was an automobile platform, and was GM's original, and oldest, platform used by all early GM products, beginning with the Chevrolet Superior. From this platform, all North American platforms B, C, and D were developed.

Starting in 1936 through 1958, GM used four different designations for various bodyshells/platforms with the A-body for Chevrolet, most Pontiacs, and the Oldsmobile Series F and Series 60. The A-body was temporarily suspended in 1958 until it was reintroduced in 1964.

For the 1959 model year, the previous A and B bodies were built on the new B Body that lasted until 1996.

The A-body designation was resurrected in 1964 for a new series of intermediate-sized cars including the Chevrolet Chevelle, Pontiac Tempest, Oldsmobile Cutlass and Buick Skylark. These later A-bodies underwent a switch in drive layout from rear wheel drive to front wheel drive in 1982. The switch in drive layout spawned the G-body. In 1997, every A-body car line was cancelled, but new nameplates on the GM W platform have taken their place.

...
Wikipedia