Prevents external contaminants from entering the system. Single-lip (the lip is the projecting rim or edge of the seal) wipers clean the rod as it retracts. Double-lip wipers clean the rod as it retracts and seals oil, eliminating "weeping" (cosmetic leakage). The double-lip wipers are secured in place with a bearing amount. These urethane wipers are metal-encased for added strength. They are often referred to as "canned" wipers (metal-encased) or "J" wipers (the metal often forms a "J" shape when viewed in the cross-section).