DO NOT GET OPEN BEARING HUBS!!! Sorry about that, open bearing are shit and will most likely break (with some exceptions in the form of the higher end shimano stuff, etc...). Also they are not nearly as smooth as sealed bearings, need more maintenance and are structurally weaker. Also I had a problem with the ACS on my bmx, where the outer ring was not very round, so dragged round the lockring, but that may just be the smaller thread ones.