The DS-KD-ACF2/S is the stainless steel two-module flush mounting bracket for Hikvision's DS-KD8003 modular door station range.
It recesses the door station into the wall and doubles as the back box, exactly as the plastic DS-KD-ACF2 does, but in stainless steel. Specify the steel version where the entrance is exposed or publicly accessible — a street door, a communal block entrance, a commercial unit — and where a plastic frame edge would be the first thing to get damaged.
Two-module size covers the most common build: a DS-KD8003 camera module plus one other, usually the DS-KD-M card reader or the DS-KD-KP keypad. That gives visitors a call button and residents their own way in, on one compact panel. If a slot is left unused, fit a DS-KD-BK blanking module. For surface mounting in stainless, use the DS-KD-ACW2/S.