If we have 3 'A' passes in an exam, We often say "I have 3As". But If we have 3 'S' passes, how to express it? I mean, is it correct to say "I have 3Ss"
If it's correct to say "I have 3Ss", how to pronounce double "s"?
If you're just talking about spoken language, the answer is simple. The equivalent of:
"I earned three As"
"I earned three Ss"
with "Ss" pronounced "esses", rhymes with "messes".
If you want to know the most idiomatic way to write it, that's slightly trickier.
First, you need to separate "3" from the grade. "I have 3As" does not mean the same thing as "I have 3 As." If you smush them together like that, it means you have an unspecified number of something designated "3A".
Second, there's the question of pluralizing the letter grades. The rule for single letters and acronyms or initialisms used to be to use an apostrophe:
How did you do on your S.A.T.'s? I got three S's.
These days, the apostrophe for acronyms and initialisms is on its way out. But many people would still use it for single letters, where it otherwise would look awkward. So in formal written English, you would most likely see:
I earned three S's.
again, pronounced "esses", rhymes with "guesses".