I have another question: what is the difference between an AD dual rear axle and a single tire rear axle?
My 1950 dually has a neat little spacer that bolts to the single wheel thus giving dual tires. I'm not sure if I have a dual or single rear axle. Was this a factory option or is this spacer a farmer idea?

1970 Chevrolet C10
Grandpa's -- My first truck -- In progress to shiny
Follow the build in the Project Journal
1950 Chevrolet 1-Ton Dually
"Ole Red Girl"
In the Stovebolt Gallery
More pictures here
1951 GMC 9430 1 ton dually--Shiny! | 1972 Chevrolet C20- Rusty- the puzzle box lid for the C10 | 1962 AMC Rambler American- my wife's
Parts trucks-
1951 GMC 9300 | 1951-GMC 9430 | 1951- Chevrolet 1300