Tapered bearings have a small diameter side and a large diameter side; this orientation is referred to as a taper. Outside of the tapered bearing rests a seal. The seal prevents contaminates from entering the bearing,while helping to retain the lubricate in the bearing. When installing an internal, tapered bearing, make sure the seal is oriented towards the outside of the hub. A raised portion or shoulder on the axle keeps the bearing from moving too far onto the axle and a threaded nut on the end of the axle keeps it from dislodging.