Measure the spindle diameter at the grease seal and the hub dia where
the seal presses in.
In other words measure the inner and outer seal diameters.
Go here Seals for Trailer Bearings | etrailer.com
and get double lip seals.
Or take your old seal to an RV parts counter and they can fix you up.
Autozone should also have it but they are usually lost without a car/truck
make/model to look it up.....