Huck,
Most trailers have an
axle and hubs which use what is called a zero-offset rim which centers the wheel over the face of the hub.
Additional to the rim diameter, you will need a width.
Finally, you will also need the correct lug pattern so that the new wheel has the right number of holes at the correct spacing.
It will be something like this: Hub and Bolt Pattern - 5 on 4-1/2" for 1/2" studs.
You could check with
Parkliner, wait for answers from other owners here and hope that theirs match yours, look for your (Dexter?) manual for the
axle, check on the
axle "beam" between the wheels for a label, or take the wheel to a tire shop.
I hope this is helpful.