The ball bearing hub does not have a locking washer, every time the axle nut is loosened and chain is adjusted for instance, the bearing play has to be fine tuned with the thin locknut. It is very important to leave the bearings slightly loose to accomodate for expansion from heat buildup. First tighten to about 30 footpounds to seat the bearing, then loosen about a quarter turn or less, assembled you should by wiggling the top of the rim feel a small play, about 1/32" sideways.
With the Timken taper bearing hub there is a lock washer that can ensure that the bearing play remains set, if the washer is bent down properly over the seal nut. With the Timken the play at the top of the rim can be smaller than with the ball bearing but never fully tight or never larger play than 1/32".