| 摘要 |
PURPOSE:To prevent a wen-shaped plating layer from forming, by constituting the bottom end part of a piston skirt such that a length in a vertical direction, obtained between an internal peripheral edge and a peripheral edge in the sectional shape of the vertical direction, and an angle of the peripheral edge are specifically formed. CONSTITUTION:In the bottom end part of sectional shape in the vertical direction of a piston skirt 3 of piston base material 2, a vertical directional length lbetween an internal peripheral edge (a) and a peripheral edge (b) is set to a value of 1mm or more. And a peripheral edge angle A forms an R-shape so as to obtain a value of 120 deg. or more and 160 deg. or less. Consequently, a wen- shaped plating layer can be prevented from forming by enabling an electric line of force to be prevented from concentrating to the bottom end part of the piston base material.
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