Patent ID: 8398350

Claim:
A bolt comprising a bolt body having a screw part, a head part formed at an upper end of said screw part, and a flange part formed at a lower end of said head part; and an unconductive ring-shaped resinous member covering a peripheral portion of said flange part; wherein said flange part has a disk-shaped flange body portion and a seat surface-forming portion having a seat surface which is extended toward said screw part from a lower surface of said flange body portion, said seat surface-forming portion has a smaller diameter than said flange body portion and is pressed against a portion where said bolt is to be mounted; said ring-shaped resinous member has an edge part which is located at a position nearer to a lower end of said screw part than said seat surface and outward from said flange body portion, an annular skirt part whose diameter gradually increases to said edge part, an upper annular portion, and a lower annular portion; said annular skirt part deforms outward when said bolt is mounted on said portion where said bolt is to be mounted and does not prevent said seat surface from being pressed against said portion where said bolt is to be mounted and forms an annular liquid-tight-sealing portion for said portion where said bolt is to be mounted; wherein said bolt body has an annular side surface formed by a side surface of said seat surface-forming portion; an annular flat surface formed between an upper peripheral edge of said annular side surface and a peripheral edge of said lower surface of said flange body portion; said annular side surface of said seat surface-forming portion possessing an outer diameter tapering from an outer diameter at said flange part to a smaller outer diameter at said seat surface; said ring-shaped resinous member does not cover said seat surface of said seat surface-forming portion, but covers said annular side surface of said seat surface-forming portion, said annular flat surface of said flange body portion, an annular side surface of said flange body portion, and an annular peripheral edge of an upper surface of said flange body portion; said upper annular portion of said ring-shaped resinous member covering said annular peripheral edge of said upper surface of said flange body portion; said lower annular portion of said ring-shaped resinous member contacting said annular side surface of said seat surface-forming portion and extending to a peripheral edge of said seat surface, forming a wedge-shaped portion; and wherein said ring-shaped resinous member is formed on said bolt body by insert molding.