Tow Hitch Ball - 50mm or 2"?

I needed to move a Blanik L23 trailer over the weekend. Using my 2"
tow hitch ball and I had a heck of a time disconnecting the two. I
knew that the Blanik trailer has what I assume is a 50mm tongue.

I was kind of surprised that my 2" ball (which works out to be 50.8mm)
would be a problem disconnecting. 8/10's of a millimeter difference
doesn't seem like enough to worry about.

What is the tolerance on a 2" setup? Is it so close that 0.8mm can be
a problem?

Thanks, John