Thanks all - good to know.  And thank you Dennis for the sizing.

It didn't strand me, so I was thankful for that.  I had just bad mouthed
the van to the gas attendant before it happened, perhaps it was revenge.
 (I was muttering about the sticky lock in the gas cap and said 'there are
many other things on the list to fix')...  sorry van!

I just pushed the plastic back onto the pegs, which was a snug fit, and
stayed on for a while.  Probably improved fuel efficiency too, as I drove
with a gentle foot.  :)