What the ratings mean for fit
The E2E-X4B212-M1 is a shielded M12 barrel proximity switch — the shield concentrates the sensing field forward, so you can flush-mount it in metal without false triggers. 4 mm range is typical for a shielded M12; enough for tight spots where a target comes in close without needing a lot of standoff. Wired as a 3-wire DC PNP, normally closed. That means the output is high when no metal is present, and it switches low when the target enters the 4 mm window. Out here in the grease, that's handy for catching a part that's worked loose — if the wire breaks or the sensor fails, the signal drops and the controller sees it.