a grease seal, two bearings, a dust cap and a cotter key. that does it, and it keeps you safe. but, make sure that when you pack the bearings, you use a high quality grease, and to be on the safe side, use a marine grease.
something else that you have to be concerned with is something that most people never pay any attention to, and that's the axle. the axle on a trailer is usually hollow, it's not solid, and they rust. like this one rusted to where the wheel fell right off the trailer. so, what you have to do is not look at just the top of the 