My experience over the decades I have lived with a half dozen or so sinks, is that a stainless
adjustable (open or closed) stopper that has small holes or slots in it for water to go through
when it is on an "open" setting, is that so far, they have all been a standard size. All of them.
OTOH, I have always had a double sink, with garbage disposal on one side. I used to buy
new ones at KMart. Now that they have closed, I will go to Ace Hardware. I have never
purchased one that did not fit, although I did mistakenly once purchase one that was only a
stopper, and didn't have the ability to stay open unless I tipped it at a slant in the drain.

N.