Does anyone know to what the green numbers stamped inside a closed element air cleaner refer? Is this something a "numbers matching" guy would even look at? The original air cleaner was damaged, but I bought a used one on eBay ($10.00!) that was identical except for the numbers.

Does anyone know to what the green numbers stamped inside a closed element air cleaner refer? Is this something a "numbers matching" guy would even look at? The original air cleaner was damaged, but I bought a used one on eBay ($10.00!) that was identical except for the numbers.

Most likely an inspector's stamp.