A fastener assembly, to be mounted upon a workpiece having a sealing surface and a threaded aperture extending from said sealing surface and through said workpiece, comprising:
- a screw having a head portion, and a shank portion integral with said head portion, said shank portion defining a longitudinal axis through said screw and being threaded for threaded engagement within said threaded aperture of said workpiece, and said head portion having an annular recess portion defined within a bearing surface portion thereof, for engaging said sealing surface of said workpiece, and surrounding said shank portion of said screw, said annular recess portion having a predetermined volume, a predetermined axial depth as defined from said bearing surface portion of said head portion to an axially recessed sealing surface of said recess portion, an outer peripheral surface, and an inner peripheral surface;
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- an annular sealing ring having an annular sealing portion and an annular web portion projecting radially from said annular sealing portion, said annular sealing ring having a volume which is less than said predetermined volume of said recess portion of said head portion of said screw so as to be capable of being entirely housed within said recess portion of said head portion of said screw when said screw is fully threadedly engaged within said workpiece, said annular sealing portion and said annular web portion of said annular sealing ring having peripheral portions which are disposed in contact with said inner and outer peripheral surfaces of said annular recess portion of said head portion of said screw such that said annular sealing ring is able to be seated and retained within said annular recess portion of said head portion of said screw prior to said fastener assembly being threadedly engaged within said workpiece, said annular sealing portion of said annular sealing ring having an axial depth which is greater than said predetermined axial depth of said annular recess portion of said head portion of said screw so as to project axially outwardly from said annular recess portion of said head portion of said screw prior to said screw being fully threadedly engaged within said workpiece as defined by said bearing surface portion of said head portion of said screw engaging said sealing surface of said workpiece, and therefore prior to said annular sealing portion of said annular sealing ring being disposed in a compressed state between said sealing surface of said workpiece and said sealing surface of said recess portion of said head portion of said screw, while said annular web portion of said annular sealing ring has an axial depth which is less than said predetermined axial depth of said recess portion of said head portion of said screw so as to define an expansion space within said recess portion of said head portion of said screw into which said annular sealing portion of said annular sealing ring can expand when said screw is fully threadedly engaged within said workpiece and said annular sealing portion of said annular sealing ring is disposed in said compressed state so as to define a seal with said sealing surface of said workpiece.