Cast Wheels

[James in Al]

I have a 1950 Model B. The cast wheels have the usual four rectangular slots. They also have four round holes cast into them. I have seen both on restored tractors. Are the wheels with both, factory or after market? What was the purpose, if any, of the round holes?

 

[430WLPG]

they showed up in mid year 1950 and the part number did not change, was some kind of a manufacturing reason