US Patent 7278810 Grommet

A grommet for an opening of a sheet member includes a shank, a head and at least a flexible locking tab. The shank includes, in a region adjacent the head and outside the locking tab, a shoulder to be placed below an edge of the opening when the shank is rotated an angle about the axis of the opening after being inserted therein. The shoulder and the locking tab prevent withdrawal of the grommet from the opening. The shank further includes an inclined outer surface section connecting the shoulder and the lower surface of the head. The inclined outer surface section engages the edge of the opening and draws the shank into the opening upon rotation of the shank.