| 摘要 |
A self tightening planar member and at least one retention member attached to the planar member. The planar member includes an inner perimeter, an outer perimeter, and defines a central axis. The least one retention member including a planar leg portion and a planar hook portion. The leg portion extends from the inner perimeter in a first direction along the central axis. The hook portion projects from the leg portion toward the central axis in a second direction, which is opposite the first direction along the central axis. The hook portion is acute to the central axis and has a free end located on an imaginary perimeter concentric to the inner perimeter of the planar member. The central axis and a plane passing through the hook portion of the at least one retention member form an angle in the range of approximately 20°-30°.
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