Steel hitch used to attach bike trailer to rear axle of bicycle.
A good use case is to get an extra hitch, so you can easily attach your trailer to more than one bicycle. Two parents, two bikes, one trailer? Buy extra hitch for the second bike.
Here's hitch as shown on Burley website. At time of this listing, selling for $25 (plus shipping).
FYI: Burley website, says "If you are upgrading from a Classic Hitch to a Steel Hitch, you will also need to purchase a Flex Connector: Part # 950038 (square tow bar) or Part # 950037 (round tow bar).