Structure of clinch portion of mounting cup

A structure of a clinch portion of a mounting cup for holding a gasket of said mounting cup clinching a can bead, wherein:

• said clinch portion includes a curl portion continuous with an upper end of an outer circumferential wall at an inner circumferential edge of said curl portion, and a curl skirt portion having an upper end continuous with an outer circumferential edge of said curl portion, respectively of said mounting cup and being concentric relative to a center line of said mounting cup;
• an inner plane of said curl portion is formed including a curved plane in an inner portion on a side of said inner circumferential edge and a curved plane in an outer portion on a side of said outer circumferential edge;
• and
• a space, into which a portion of said gasket can enter, is formed between a virtual curved plane with a single radius constituting the inner plane of said curl portion and said curved plane in said inner portion or said curved plane in said outer portion, wherein a radius of said curved plane in said inner portion or a radius of said curved plane in said outer portion is set differently from the radius of said virtual curved plane, wherein the radius of said curved plane in said inner portion is 40-80% of the radius of said virtual curved plane.