This large grommet is so hidden, most owners have no idea it exists. It is exclusive to the 1947-55 (Advance Design) Suburban, panel truck and Canopy Express.
Because the body is so much wider than a step side pickup the full add pipe must be longer. The body also has an inner as well as outer panel. The inner panel protects the outer sheet metal from accidental damage when merchandise with sharp corners is hauled.
To prevent metal to metal contact from the gas spout touching the inner panel, GM provided a different grommet for inner and outer metal panel. It is the unseen inner panel that has the seldom seen grommet.
Check these photos. They show the inner grommet in position as well as on a table for photos.
Above data made possible by allowing US a close view of this 1948 Suburban. The owner Jerry’s Chevy Restoration Shop in Independence, Mo.