Re: mismatched balls and couplers
I've been out and about and found the need to tow something home and only had my 1 7/8" ball with me, I simply tightened down the coupler adjustment till it fit snug and headed home. It wasn't right but it sure beat driving 20 miles back to the house to get my other hitch, or buying a new one on the road someplace. Besides, in more than one case, it was first come, first to get it with a free boat or trailer, leaving may have lost me the deal.
I do now carry several sizes in my truck, and car.
I have an old garden tractor I use around the yard just for moving trailers, its got an old rusty 1 7/8" ball on the back, I hang any size coupler on it, so long as there's tongue weight, they don't go anywhere. I wouldn't try that on the street though.