| CPC F16J 15/067 (2013.01) | 17 Claims |

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1. An attachment structure, comprising:
an annular metal seal;
a first member having a first planar surface;
a second member having a second planar surface;
an annular seal groove recessed in the first planar surface, the seal groove having
a rounded inner corner portion, and
a side surface connecting continuously with the inner corner portion; and
a positioning ring configured to be disposed in the seal groove with the annular metal seal, for positioning the annular metal seal, and be separatable from the annular metal seal, wherein
the annular metal seal is configured to be fitted in the annular seal groove and is deformable by the first and second members fastened to each other, whereby the first and second member are sealed at the annular metal seal,
the annular metal seal includes an annular seal body, the seal body having
a side surface facing the side surface of the annular seal groove, and
an outer corner portion that is at an end of the side surface of the seal body and that forms a ridge, and
the positioning ring is configured to be held between the side surface of the seal groove and the side surface of the seal body, and is configured such that the positioning ring abuts on at least a portion of the side surface of the seal groove, whereby the ridge of the seal body is positioned away from the side surface of the seal groove so as to be free of contact with the inner corner portion of the seal groove, when the first member and the second member are fastened with each other, whereby the first and second member are sealed at the annular metal seal.
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