The gain protectors are designed to easily adjust the gain knobs without accidently changing another channel while still being able to adjust the PAD switches. Also, it will prevent the gain knobs from rotating while doing field work, for example sleeves, fabrics or other objects that come close to the ZOOM H6.
It fits perfectly in place of the standard cover of the ZOOM H6. Just unscrew and replace will do.
The allignment of the numbers with the arrows might not be perfect and is different for each device. Therefore it is possible that the holes in the model aren't perfectly in line with the numbers on the ZOOM.