if you have the stock type bearing it comes in two pieces, the bearing and a thin spacer and a larger retaining ring/oil seal sealing surface,the small ring goes on first with the inside rounded part going twards the four bolts on the axel, then the bearing, if the bearing is from napa auto parts or some other place put the bump on the back of the bearing tward the four bolts,if you plan on going to the rubicon put some loc-tite bearing retainer on it frst so your bearings do not come off the axel while driving, then put the larger retaining ring on next with some loc-tite with the outside rounded edge twards the splines on the axel, you will need a press to do this or have it done. the seal goes in the axel tube. oh ya almost forgot, make sure your backing plate is on there first or your sj-410 retainer. or if you have disk brakes never mind.