Ed,
Opps, well you will now have a set of galley plugs. From your last post you do need Expansion plugs, freeze plugs, soft plugs and or welch plugs to use just a few different names for the same thing.
If the shop tells you there are 5, three on the side and two at the back then expansion plugs "are" what you needed. Ron called it correctly. Steel (zinc plated) is 100% good.
Dorman is a common brand, size is 1-21/64" Dorman part number is 555-072. Napa (seal power) part number is 3812127. Even easier to come by.
Dug