The description seems right although I don't know the size off hand. The photo looks a bit odd because it doesn't have sides to it. I think the photo is either generic or there is a shadow from the flash that looks like it has a side to it. Anyways, calling it a disc is how I would describe it.

1951 GMC 1 Ton Flatbed -- It is finally on the road and what a great time I have driving it!
1951 1 Ton Completed

My Chevy Master 4 Door is on the Road!