A failed sensor run at 2 a.m. usually ends with someone holding a replacement cable under a work light, comparing the small plastic face inside the coupling nut against the socket on the machine. That face is the coding, and it decides whether the cable will seat at all. M12 A-Coding and D-Coding look similar from arm's length — same 12 mm thread, same screw locking — yet they are built for different electrical jobs. Once you know what to look at, telling them apart takes seconds, and it removes the temptation to force a plug that almost fits.