3. Why 4M Sizes Differ Between Brands
3.1 “4M” Is Not a Universal Mechanical Interface
The “4M” designation does not guarantee a shared mechanical interface. Products from different brands or series may have different plate dimensions, mounting structures, screw-hole spacing, and box-depth requirements. Confirm these dimensions individually before replacing an existing switch.
Brand differences may result from several design decisions:
Module width and module pitch may differ between product families.
The decorative plate may be designed to be slim, wide, square, horizontal, or vertical.
The mounting frame may use horizontal screws, vertical screws, clips, or a proprietary locking structure.
Metal box flanges and folded edges can change the external size without increasing usable internal volume.
Smart modules can require more rear space than conventional switches.
Some systems are designed around a dedicated matching box, rather than broad retrofit compatibility.
3.2 Screw-Hole Spacing Is Often the Failure Point
The visible plate can hide a wall opening, but it cannot solve a screw-hole mismatch. If the new smart switch frame has mounting holes at a different center-to-center distance from the existing 4M box, installers may face one of four outcomes: the product cannot be fixed, the frame sits under stress, the plate becomes uneven, or the team modifies the box on site.
For a B2B project, modifying boxes after wall finishing is not a minor adjustment. It can create rework involving electricians, wall repair, repainting, delayed handover, and customer complaints. This is why the screw-hole center distance should be treated as a mandatory pre-order specification, not an optional technical detail.
3.3 Smart Switch Depth Changes the Decision
A 4M wall box that accepts four conventional modules may still be unsuitable for a smart switch. The decisive measurement is not only the specified nominal box depth. It is the remaining clear depth after wires, connectors, conduits, and loop-through conductors occupy the cavity.
For example, a box may be nominally 50 mm deep, but if cable entries are crowded and several conductors are bent behind the switch, the usable space can be far less. A smart switch with terminals at the rear may then press against wiring, prevent the frame from sitting flush, or create unacceptable stress on the conductors.
