Structure for screwing object on sheet metal

Claim 1

A structure comprising a screw and an object having a fixing hole and a piece of sheet metal to which the object is fixed by said screw extending through said fixing hole comprising: said screw having a screw head at one end having a diameter larger than that of the fixing hole for engaging one side of the object, and a shank having a substantially uniform diameter, said shank integral with and extending from said screw head and having an external thread on the outer surface thereof, said thread having a following flank facing said screw head forming one side of said thread and extending substantially perpendicular to the outer surface of said shank and a leading flank forming the other side of said thread meeting said following flank at a predetermined angle, said thread extending spirally around the outer surface of said shank so that the spacing between the turns of said thread along the outer surface of said shank has a predetermined width as measured in the direction in which the shank extends; and the piece of sheet metal having a surface for engaging the other side of said object, a receiving hole therethrough, and an annular lip of uniform thickness having in inner circular edge defining said circular receiving hole and an outer circular edge at which said annular lip is bent from the surface of said sheet metal away from the object and at a predetermined angle relative to the surface of said piece of sheet metal so as to form a frustrum shaped depression at the surface of said sheet metal open to and communicating with said receiving hole, said shank of said screw extending through said frustrum shaped depression and said receiving hole so that said annular lip is engaged between said following and leading flanks of said thread to mate therewith for attaching the object between said screw head and said surface of said piece of sheet metal.