In Canada and the US, there are entire networks of stations which are designed to only fuel large commercial trucks.

They tend to be cardlock systems - i.e. they aren't staffed during most times, and the customers require existing accounts to use them.

They are large enough to accept the largest trucks, and have room to maneuver those trucks. The pumps are fast, and supply high volumes. I expect that they have larger nozzles.

The attached image is taken from the website of one of the many companies that compete for the commercial truck business - it gives a sense of their scale.

In addition to the suppliers that cater just to the large commercial truck business, many of the retail petroleum stations that are designed to serve personal automobiles and small trucks offer diesel fuel as one of their product choices. Their dimensions and layouts are more suited to smaller vehicles, and their pumps are similar. It is stations of this type that the OP was most likely inquiring about.