Fuel-dispensing nozzle inhibitor

A nozzle inhibitor (10) is positioned in a filler neck closure assembly (11) to prevent a user from pumping unleaded fuel into a diesel fuel tank. The nozzle inhibitor (10) blocks full insertion of a small-diameter unleaded fuel nozzle (20) into the filler neck closure assembly (11) yet allows full insertion of a large-diameter diesel fuel nozzle into the filler neck closure assembly (11).