There are 2 nozzle sizes used for diesel depending on where you go - we had a guy working at a servo come out wondering how I'd put diesel in the xtrail where it apparently shouldn't have been cause I'd used the high flow (truck) pump rather than the car one. I had to show him the glow plug light when I started it before he stopped panicking that I'd put the wrong fuel in it...The diesel nozzle won't fit into an unleaded vehicle, but no problems getting unleaded into a diesel.
They are very obviously different sizes, but diesel does use both...