What is a double promo? Well, we start off with a dealer promo model car or truck. That's a standard auto dealer promo. One the next level we have a double promo. This is the standard promo plus an additional promo item. It could be a 1966 Chevrolet in orange with Budget-Rental Car logos and script. Then comes the triple promo. This could be a 1966 Olds Toronado for the Bing Crosby's Pebble Beach Pro-Am. Finally, there is the quadruple promo. I know of only one. It is a Divco step-van with a placard for the "Milkman" movie circa 1950. On the placard are two Hollywood personalities: Frank O'Conner and Jimmy Durante.
At this time...er....coming in a week or two will be a double promo for sale here. It is not a car. It is an Allis-Chalmers bulldozer with a Baker (brand) blade. The scale is likely 1/16th and it was made by Product Miniature Corporation, which also made International and Diamond T promo trucks and Chevrolet, Plymouth and Nash cars back in the 1950's.
I have discovered the Milkman Divco for sale at a future auction. It has been splattered with something ugly looking, but it is only the second one I have ever seen. Here is a photo of it.