It’s surprising that an item placed on almost every 1947-55 Chevrolet and GMC truck has become so impossible to locate. Most collectors have never seen one!
The product is the five inch GM round mirror head. It was originally bolted to the cowl mounted mirror arm on the driver’s side. They were always black and had the pivot on the outside (most round similar non-GM mirrors have the pivot inside the housing).
The pictured mirror head is New Old Stock. Even the zinc plating, which reduces rust, is perfect. The acorn nut can be tightened just right so the head is still hand adjustable yet will stay in place on rough roads.
If almost 500,000 Advance Design trucks were produced each year between 1947-55, where are the original mirrors? The answer relates to the use of the vehicle. These trucks were made for work! Few were garaged. After several years of weathering the mirrors were in need of replacement. This was an easy do-it-yourself exchange and most owners could pay less for aftermarkets at an auto parts store or service station. Few genuine GM replacement mirrors were bought and thus the dealer kept very few if any in stock.