The International AI is basically the same tractor as the Farmall A. I stands for industrial and the tractor will have a foot throttle and heavy duty diamond shape front axle. The heavy axle was also an option on the Farmall. The two tractors along with the B share a common set of serial numbers. These tractors were all built between 1939 and 1947. The post 1947 tractors all had touch control hydraulics.
The A and AI were about 17-18 hp, C-113 engine as in 113 cubic inches, magneto ignition, 6 volt positive ground, some of the very first A and AI did not have a starter or battery. The rear tires were 8x24 and 5.00x15 front. They were available with pto and belt pulley. 4 speed transmission. Serial number should be under seat on left seat support. The engine serial is stamped on a machined flat surface just below No. 1 spark plug. There are lists available telling year of manufacture as per serial number.