Got a trailer? We have three of them in the side yard here (had four, but my pal Mike took his boat to Cape Cod with him). Of those three, one is an old generator base and has Dayton style wheels (the 1 piece rims where the spokes are integral to the hub, usually only found on mobile homes these days).
The other two take normal white metal consumer trailer wheels.
But what kind of trailer wheels? They come in different sizes, and it costs about the same to buy a new mounted wheel as it costs to buy a new tire and have it mounted on the old rim, so most people go with just buying the replacement wheel and tire as a unit.
Fortunately, the people at Reliable Production Machining and Welding have this cool trailer hub bolt template that you can print out and use on your wheels to figure out what you're looking at before you head off to the store or buy online (local copy here).