You can’t really call them corks when they aren’t made of cork. Note that box on the right, which says “Corks” on it actually contains real corks, made from the bark of the cork oak (which should be called Quercus corkus but is actually Quercus suber). These brown stoppers are made of gum rubber and are good for all sorts of stoppering needs. These are in a drawer in a small cabinet that has a fairly wide variety of things in it. As you can see, a few of them have holes cut through them. Dad used them in his home lab and I’ve found a few uses for them myself, over the years.