The serial number is located on a small metal plate about the size of a business card. On "styled" Model B tractors it can be found on the top surface of the transmission case, on the right side of the tractor (as you sit in the seat), just below the magneto or distributer.
The plates were usually made of aluminum, although during the war they were made of steel and they rusted quite badly. If the plate is rusted and you can't read it, you have a tractor that was probably built around 1944.
On the "unstyled" Model B tractors the serial number plate is found on the left, or flywheel side of the tractor. It's on the SIDE of the transmission case, in the FRONT corner. You can't MISS it!!.
On OTHER models of two-cylinder tractors, the serial number plate might be located in another spot. Just look around. You'll FIND it!!
If the serial number plate is GONE I'm afraid there is NO other way to determine the serial number of the tractor. The best thing to do in that case is go to THIS page and possibly narrow down what the year of the tractor might be.
Oh, by the way, I had heard that on some of the VERY early "styled" tractors (serial numbers in the early 60,000's) the number plate is found on the same side as it is on the "unstyled" tractors. The owner of Model B #60,019 says that his number is under the magneto. Does anyone have an EARLIER styled tractor where the number is on the flywheel side??