The serial number on a Farmall M tractor is on a metal data plate on the left side of the engine compartment. The plate is roughly halfway between the front and rear of the engine housing, almost directly below the Farmall brand name lettering.
The serial number on a Farmall H tractor is on the transmission housing on the left side of the vehicle. While the plate on the Farmall M is silver-toned metal with a black rim, the H series plate is all black. The Farmall Super M's serial number is on the left side of the clutch housing, also on a silver-toned metal plate. All three tractors were products of the International Harvester Company and are no longer in production.
The engine serial number may be required when ordering parts for the tractor's engine. Look for a stamped number on a flat portion of the cylinder block. The engine serial number should be similar to the tractor serial number, but slightly higher in the same series of numbers. The stamp is typically located on the tractor's left side, under the valve tappet cover.