The lightest B+W Neutral Density Filter attenuates the light by one f-stop (log density 0.3), which can be beneficial, for instance, for the correct exposure of high-speed films when the brightness of the subject is still too high for the fastest shutter speed and the smallest aperture. It is recommended especially as a complement to B+W Neutral Density Filter 102 for fine adjustments. The filter factor is 2x.
Multi-Resistant Coating (MRC): MRC by B+W is not only an extraordinarily effective multiple layer coating, it is also harder than glass, so that it protects filters from scratches (for instance when cleaning the filters), and it is also water and dirt repellent, thus facilitating filter maintenance.
B+W diopters use a thicker mount than the standard F-Pro mount, to allow for the thicker glass dimension used.