This may be the dumbest of the dumb questions. I replaced a tire with rim on my small trailer last night and while the 4 holes matched up and I was able to get the tire on just fine I noticed the center part of the rim where the hub protrudes through the rim had more "wiggle" room than the rim I just removed. Not a lot -maybe 1/16" all the way around, but the older tire didn't have that room.
I checked a number of hub assemblies and while they come in a variety of sizes to match your spindle they don't make any mention of the size of the hole in the center of the rim.
Does any of this matter. Like I said, the tire went on and is secure meaning all 4 bolts fit nicely and cranked down tight with no problem.