I can never get the pressure high enough to overfill a gas tank. They're usually very thick walled and the gauge on the inlet lets you know the pressure. It's basically fool proof, unless you drop it and the valve comes off, but they all have that rail around them now which also makes a great carrying handle.
In my youth I managed it on a few cars. Problem was that back then the nozzles didn't have an auto cut-off and girls were just discovering the mini skirt.Assuming gas = fuel then on what vehicle are you able to overfill the fuel tank..?