So, in these circumstances, every noun is uncountable, isn't it?

@Sergey: Whether a noun is countable is a property of the word, not the usage in some sentence. Generally, any noun word is either countable or not countable. The dictionary definition indicates which one. (A few words have usages that include both the countable and noncountable cases. If so, the dictionary will indicate both, sometimes each separately according to usage in the definition. Consider wine and sand.) The word chair is always countable, regardless of usage in the sentence. If it seems uncountable, then the reason is that the grammatical context requires a singular form.

@SergeyZolotarev Every noun can be understood as a category in the singular yes. A type of coffee, A type of boat, a type of chair. A type of missile. epi is mistaken. Boat, chair and missile are usually countable. [Of course, coffee can also be countable.]

@Lambie: Refer to explanation for uncountable: "A noun that cannot be used freely with numbers or the indefinite article, and which therefore usually takes no plural form." Note the distinction between the noun, and its form.

I suggest that you provide references to authoritative grammar sources to support your respective positions (available online)

@SergeyZolotarev If you memorize my examples, you'll have everything you need.My specific answer is for your specific question with type of. Believe me, you will not need anything else. Conclusion: one type of [plural noun] = BUZZER.

@Lambie Could you provide a source? I'm not implying that you're wrong, but I would like to see one

@Lambie: My first comment narrowly addressed Sergey's question. It had no further relation to your answer. You chose then to argue that chair has uncountable usages. My other comments addressed that claim. Since you appear to be, for some reason, upset by this exchange, I'll leave to others to decide what is clear, accurate, or useful.

@SergeyZolotarev For what?? A type of [plural noun]? You can't prove a negative. Or, for a countable noun used as a category? All English speakers know that instinctively.

@epi Your comment has nothing to do with my answer. If you want to address his question, put your comment under his question and not under my answer.

I would like to see a grammar source that says something along the lines of, "All nouns are treated as uncountable nouns if they are used as categories after phrases like 'a type of', 'a sort of', etc."

@SergeyZolotarev Good luck with that. a/an x is singular. s is plural. types of, sorts of. Naturally, what comes after "of* in the singular a type of has to be singular.

The confusion is that you seem to mean that the word appears in a singular form, which is clear and accurate, but you explain it as the word becoming uncountable, which is unclear and unsupported.

(Also, the suggestion that English speakers know "instinctively" how to make a plural form, but none has ever created written instructions in a reference guide, seems to be easily refuted by a simple web search. I would suggest using the search keywords "english plural", if you feel unsure where to start.)

@epi Merriam Webster: 1a: a particular kind, class, or group = pretty much a category. And "one type of" can only be followed by a singular noun.

I'm not following the meaning of your comment or how it might relate to any open question. If I may offer a suggestion, you might replace, in your current answer, the word "non-countable" (which anyway is not preferred, in contrast to "uncountable"), with the phrase, "appears in the singular form". I believe that even such a small change would resolve the entire confusion.