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July 19, 2015 at 11:56 pm
#20428
FYI – when searching for disc-shaped plugs of this type, the following terminology may be of use.
Plugs that are convex (domed) on the outer face are generally termed ‘Welch plugs’, and they are slightly undersized. They are always driven up against an internal shoulder, and seal by expanding radially as the dome is pushed inward.
Those plugs that are concave (dished) on the outer face, often with deep rims, are termed ‘core plugs’ or ‘frost plugs’, and they are slightly oversized. They may or may not be driven against an internal shoulder, and seal as the rim compresses in the slightly undersized plug hole.