Today, I drive down to Costco, to fill my trunk with 50 gallons of gas:
https://c4.staticflickr.com/4/3892/1...7df1c083_b.jpg

When, lo and behold, I smell strong gas fumes while driving.
So, I pull over, and open the trunk, and what do I see?

Yet another plastic spout cap broke along the perimeter:
https://c2.staticflickr.com/6/5559/1...47f6daf7_b.jpg

So, I stop by Lowes to pick up a replacement 5-gallon portable storage can:
https://c2.staticflickr.com/6/5557/1...91f0eeca_b.jpg

Resigning myself to transferring the gas from the old can to the new
can, lo and behold, I find that the new cap seemingly fits the old
threaded neck, yet, the converse isn't true.
https://c4.staticflickr.com/4/3882/1...71ae219f_b.jpg

The old spout doesn't seem to fit the new can's threaded neck. Huh?
https://c4.staticflickr.com/4/3868/1...2b1332bd_b.jpg

I ask: How can it be that the new spout fits the old can, but that
the old spout doesn't fit the new can?
https://c4.staticflickr.com/4/3894/1...38b485eb_b.jpg

One reason it matters is that I have more than a few of these
one or two year old gas cans where all the spouts break the same!
https://c4.staticflickr.com/4/3924/1...4ce3cb93_b.jpg