The phrase "a single category of" is correct and usable in written English.
It can be used when referring to one specific group or classification within a broader context.
Example: "In our research, we focused on a single category of species that exhibit unique behavioral traits."
Alternatives: "one specific type of" or "a distinct group of".
He favors some form of worker participation, and, like Mulcahy, advocates creating a single category of employment.
To lump opponents of Wall Street or international treaties into a single category of anti-Semitism reveals either intellectual confusion or intellectual dishonesty.
And he said he would invest only in a single category of start-up, known alternatively as "software as a service" or "on-demand computing".
To focus their analysis, the researchers chose to look only at a single category of patients: elderly people with heart failure.
Its main feature was reducing land tax and corvée obligations to a single category of payment in bulk silver or its grain equivalent.
They raise distinct constitutional issues, and together could go far toward defining what limits apply and what justifications are needed when the government carves a single category of criminal offenders out of all others for especially burdensome treatment.
Counting the use of only these two words in a single category of Presidential speech may be the sort of slapdash statistical analysis that sets Nate Silver's teeth on edge.
To prevent the day bag from morphing into an impossible black hole, she suggests a system of pouches in various sizes, each devoted to a single category of items (like makeup), which can be labeled or color-coded, then tossed into the tote (or stored in the "deep drawer" when not in use).
I know in my own writing that the term "hybrid essay" helps me avoid the perilous task of trying to fit my work neatly into a single category of nonfiction: personal essay, memoir, lyric essay, meditation, braided essay, literary journalism, biography — pick just one.
