I have a collection of wheels and casters, mostly picked up in yard sales.
I have way more than I will ever use. I could quit collecting them if I
wanted, so I am not addicted.

From time to time, I have used shopping cart wheels. They're pretty good
for lighter stuff. My local scrap yard sells them rather cheeply--they're
from carts that got run over.

Ciao,
David Todtman