Which proximity sensor to use? I am building a dolly and I am confused as to which proximity sensor to use. 

Should I go for M8 or M12 and 5&nbsp;V or 6-36&nbsp;V? 

What should be the best detecting distance? Should it be 2/4/8&nbsp;mm. Which one should I select?
Tomas Sanladerer has produced a nice video on this topic: https://www.youtube.com/watch?v=il9bNWn66BY

@ 7:31 you see an overview of the precision of various sensors, including the ones you mention. It appears that the M12-4 and M18-8 sensors are more accurate than the M8-8.