Fuel Filler Hose: Description and Operation

Purpose:
To help prevent refueling with leaded gasoline, the fuel filler neck on gasoline engine vehicles has a built-in restrictor and deflector.

Operation
The opening in the restrictor will only admit the smaller unleaded gas nozzle spout, which must be fully inserted to bypass the deflector.
Attempted refueling with a leaded gas nozzle, or failure to fully insert the unleaded gas nozzle, will result in gasoline splashing back out of the filler neck.