Used to be a 2" ball here - still some trailers around with 2" hitches. I was hoping my old 50mm hitch on my old car transporter trailer would drop on the new 2" ball mount I bought in the US for my Challenger . . . but no. Had to find a similar style of bolt on ball but 50mm in Germany to replace it.Unfortunately "over here" we have 3 sizes:
1. 1 7/8"
2. 2"
3. 2 5/16"
Mixing up #1 & #2 is pretty easy to do, and causes problems.
When I re-did the small black trailer last summer, I removed the 1 7/8" hitch,
and replaced it with a 2" so I do not own a single 1 7/8" trailer anymore.