A knockout has a support surface and the support surface has: (i) a first knockout outer diameter capable of supporting the first inner diameter of a container side wall when the knockout is inserted into an opening of the metal container and when the metal container is being necked with a necking die; and (ii) a second knockout outer diameter capable of supporting the second inner diameter of the container side wall when the knockout is inserted into the opening of the metal container and when the metal container is being necked with the necking die, and wherein the first knockout outer diameter is larger than the second knockout outer diameter.
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