Follow the installed system, not preference: the tip diameter is fixed by the probe bore in the bearing housing and by the calibrated linear range your Proximitor was set up for. 8 mm is the standard for most sleeve-bearing machines; 5 mm appears where the mounting hole is smaller or where a smaller linear range is wanted. If you are replacing one probe of an installed set, order exactly the part number already there — mixing diameters in one measurement channel is not supported.
