U-Cup 

U-Cups (U-Packing or U-Ring) are the most compact and versatile of the many lip type seals available. In its several configurations, it may be utilized as an ID - Rod Seal, or an OD - Piston Seal. U-cups with long thin lips may exhibit very low dynamic friction and can accommodate out-of-round or eccentric components.  Shorter, heavy, lips provide a more reliable seal at low pressures and are better suited for sealing at high pressures.