Patent ID: 8407996

Claim:
A cup seal held in a recessed portion of a cylinder having a tapered surface, in which an open end portion of a side wall expands toward an open end, and formed in a U-shape in cross section, comprising: an annular base portion extending in a radial direction and through which a slide member penetrates so as to slide; an annular inner lip portion extending in the axial direction from an inner peripheral end of the base portion and through which the slide member penetrates so as to slide; and an annular outer lip portion extending in the axial direction from an outer peripheral end of the base portion and coming in detachable contact with a bottom wall of a recessed portion; wherein the inner lip portion has an inner peripheral surface which at least includes a first tapered inner peripheral surface which extends in a manner that an inner diameter thereof gradually decreases forward in the axial direction from the inner peripheral end of the base portion, the inner peripheral surface has a second tapered inner peripheral surface which extends in a manner that an inner diameter thereof gradually increases forward in the axial direction from the first tapered inner peripheral surface; and a projection protrudes in the axial direction at a tip portion of the inner lip portion so as to determine a position in the axial direction when the tip portion of the inner lip portion comes in contact with an opposing side wall having a tapered surface with an open end portion expanding toward the open end of the recessed portion.