Gasoline Fuel nozzle has about half an Inch wide
Auto diesel nozzle has very slight wider than half an inch, (Started around 2007)
Trucker diesel nozzle about an 1-1/4 inch.
Really until 2007, it is impossible to use Diesel into Gas fuel vehicle thats made after 1976. The only way if it happens before 2007 is probably a funnel. But if it is after 2007 then it may be mistaken using Auto diesel pump wriggling into gas or using funnel, whats even worse it is easier to funnel Auto diesel nozzle into gas inlet.