The phrase "a single knob" is correct and usable in written English.
It can be used when referring to one specific knob, often in contexts related to controls, furniture, or devices.
Example: "The new appliance features a sleek design with a single knob for easy operation."
Alternatives: "one knob" or "a lone knob".
Instead, it's controlled by a single knob that toggles through audio, navigation and vehicle functions.
"I could not turn a single knob on any door, or any faucet, or the stereo or the television set," Ms. Robertson wrote.
In another friend's apartment, hoping for a cup of coffee, I found myself outsmarted by a high-end glass cooktop that was designed without a single knob or switch.
Others have been puzzled by the design of the company's new interior control system, iDrive, which unifies a dizzying array of functions into a single knob and has left some drivers scrambling for the manual just to start a new BMW.
"It was like disassembling a complicated machine only to discover that it's controlled by a single knob," Perron says.
In the middle of the black metal grille on front there's a single knob that's surrounded by a blue light when the speaker is powered on.
Except for prominent heterochromatin of pericentromeres and terminal nucleolus organizing regions (NORs), a single heterochromatic knob occurs in P. enysii and two knobs were found in P. exile.
Invoices show $800 was spent on a single door knob.
There are no iPod stations here; piped music (doo-wop, natch) comes through the original ceiling speaker, with volume controlled by a single Bakelite knob.
And truth be told, many of the complaints about the 7 Series were about the car's interior and controls, including the bewildering I-Drive system, in which a single silver knob was toggled and rotated through a confusing menu of radio and heating configurations.
Look to the high-res display and you can control your music (XM, Aux-in with iPod/iPhone dock, 6-disc CD/DVD), navigation and communication device; all from a single rotating knob situated underneath the shifter.
