sleeve ironing board cover_peva tablecloth with flannel backing

The oil seal gets its structural stability from an interior metal ring which serves as an inner skeleton. The outer skin is made of a more flexible material like nitrile rubber or other materials based on the physical environment of the seal. A spring on the lip of the seal supports the lip and keeps the lubricant from leaking. The lip construction is what blocks contaminants from outside.

If the seal is being fitted to original equipment you may have some influence over the shaft and housing bore finish, but if you are replacing a worn seal you still need to take into account the condition of these 2 essential parts.