The back of the hubs on my trailer have some "bumps" which I'm not sure what they are for.
The hub is a 5 lug x 5½" bolt circle diameter. From the view in the photo, the lugs are the outermost bumps which I've marked with "L".
The other bumps marked with "?" are what I can't identify. Measuring them as though they were lugs, they seem to have a 4½" circle diameter.
Note that I've been told these might be agricultural rims & axle, although this is just a normal non-ag utility trailer.