| 摘要 |
A circular inner knockout and a non-circular outer knockout formed in a wall are individually connected to the wall by frangible webs located opposite from one another. The frangible web connecting the inner knockout to the wall is stronger than the frangible web connecting the outer knockout to the wall. The periphery of the outer knockout includes by a plurality of interconnected discrete circular curved portions, and does not completely surround the inner knockout.
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