Hockey puck cut in half, used to stabilize a wheeled trash bin on a slope.
https://diqn32j8nouaz.cloudfront.net..._trash_bin.jpg
Previously:
https://www.homemadetools.net/forum/...409#post211882
https://www.homemadetools.net/forum/...738#post174835
https://www.homemadetools.net/forum/...287#post138723
https://www.homemadetools.net/forum/...402#post154618
