Often found on the front bolster (the casting holding the front axle) or the main frame channel.
Serial number ranges vary significantly across models. For many early-to-mid 20th-century models, the serial number "501" frequently designated the first unit built in the first year of production. Starting Serial Number Case Model 10-18 Case Model 10-20 Farmall A, B, BN Farmall Cub Farmall 140 International 384 How to Decode IH Serial Number Tags International Harvester Tractor Serial Number Table-