I saw a question in another elsewhere about replacement bearings and hubs for the Harbor Freight frames. I answered the question there, but I'll repeat the answer here since I've used HF frames under both of the trailers in this thread.
You could order replacements from HF, since the bearings are metric, but it's a lot easier than that.
The spec for the HF bearings is 30205 Taper Wheel Bearings, 25mm i.d. x 52mm o. d. x 16.25mm thick
. Here's a link to replacement bearings on amazon: http://www.amazon.com/30205-Taper-Wh...keywords=30205
Many/maybe most 2000-lb. or less trailer axles have 1" spindles. I have a pair of spare Dexter 1250-lb. (each) hubs here, the bearings are 1" I.D. The spindles that came with the Dexter hubs measure 0.980 O.D.
The Harbor Freight spindle measures 0.979, which is only 0.001 less than the Dexter spindle. (25mm is 0.984 BTW). Because trailer bearings/spindles are designed for an easy slip fit, and because there's only one thousandth of an inch difference in the spindle diameters, hubs designed for 1" axles will fit very nicely on the Harbor Freight axles. In the photo below a Dexter hub with 1" I.D. bearings is on the HF axle; the HF hub in on the floor. It's a very good fit, if you didn't know the Dexter bearings were 1" and the HF axle was 25mm, you'd never be able to tell when you installed the Dexter hub on the HF axle.
1250-lb. hubs can be bought complete with bearings/seal/cap/lug nuts for around $35, here's one: http://www.northerntool.com/shop/too...2391_200442391
. I wouldn't hesitate to use one of those hubs on a Harbor Freight axle based on my fit test.
Swapping to the US-spec hubs has another benefit, it would get you 1/2x20 lugs, which are the same as the Wrangler. The HF hubs have 12.5mm lugs.
And another benefit would be that you'd be able to pick up replacement bearings for the US-spec hubs anywhere, the metric bearings can be harder to find (and the metric outside diameter of the bearing is important for fitting it into the hub, US-spec 1" I.D. trailer bearings won't fit properly in HF hubs.
BTW, the HF 4-on-4 hubs used on the lighter-duty trailers and the HF 4-on-5.5 hubs used on the 1720-lb. capacity trailer both have bearings with 25mm I.D. This means that the hubs I linked to above could be used to upgrade a 4-on-4 HF axle to a 4-on-5.5 (same as the TJ/YJ Wranglers). Be careful about larger tires though, because the lighter capacity HF frames have sheet metal u-channel axles, while the 1720-lb. capacity HF frame has a much stronger tube axle.
Edit: One more thing about putting US-spec hubs on the HF axles - the inner oil seals on the US hubs may not seal well enough on the HF axles, so you should check them when you're installing the hubs. Most US-spec 1" O.D. axle spindles have 1.25" O.D. sections for the oil seals, and the HF axles are 1.18" where the oil seals run (30mm), so the US-spec seals may or may seal well enough, depends on the particular seals.
Most U.S.-spec 1.25" I.D. trailer seals are 1.98" OD, which right about 50mm, so you might want to replace the US-spec oil seal with a 50mm O.D./30mm I/D. metric one for a better fit. Here's one: http://www.amazon.com/Amico-Spring-L...50+mm+oil+seal