If it goes on a 2", then that's the correct size.

 Usually the ball size is stamped right into the coupler.

I assume it would be 2-inch.

When my sister purchased her teeny-tiny Viking camper a couple years ago, the
hitch installer equipped her TV with a 1-7/8-inch ball.

Back at the RV place, we hitched-up and clattered and banged all the way to
the hitch place to swap it with a 2-incher.

Good luck!

Unless the coupler has been changed, it's a 2" ball.

Austin