What is the appropriate fitting to connect an armored cable to this stand-alone receptacle product?
That is not the right clamp
The clamp/fitting you have is a two-screw type clamp designed solely for use with nonmetallic-sheathed cables (NM, UF, and perhaps SEU/SER).  Instead, you need an armored-cable fitting that fits a ¾&quot; KO and is of the right size to accept the outside diameter of your cable; there are several styles available, but the one you're most likely to find at a hardware or big-box store looks like the Arlington Industries 8402 depicted below: