The various carburetor companies used a variety of methods to plug access holes needed to machine passageways.
Carter used copper drive plugs in the 1930's, which were superseded by aluminum plugs in the early 1950's.
Rochester, Stromberg, and Zenith used lead balls.
I don't know about Holley, as I never would work on one.
The plugs will eventually fail. With Carter, a good idea to tap the plugs with a drift punch and a hammer when rebuilding the carbs. The plugs are tapered, so tapping them will make them tighter.
With the others, either wait for them to fail, or dig them out and replace then when rebuilding.
As Jerry mentioned, a split shot sinker maybe a third larger diameter will work.
For those requiring show appearance, we have most of the various sizes of Carter plugs available if our minimum sale is ordered.
Jon.
