Actually, some servos have 2 different sized diesel pumps.
A few Caltex servos near me have a larger quick fill pump and a very unleaded sized diesel pump, I presume for VW's etc.
The small pump is even on the same bowser as the 91RON unleaded. When compared, I could not notice the difference in size between the pumps...
Having said that, seriously. How can you not look which pump you have picked up?
I mean, it's you pride and joy man!