The usable internal width of the DIGITUS DN-10-09U wall-mounted enclosure when the two rails are removed corresponds to the internal width of the enclosure minus the dimensions of the rails.

- The internal width of the enclosure is 312 mm.
- The rails are part of the 254 mm (10 inch) grid dimension construction, but the exact width of the rails themselves is not explicitly stated. However, the width of the rails is usually part of the grid dimension and not in addition to it.

As the rails are integrated directly into the grid dimension and do not take up any additional width beyond the grid dimension, it can be assumed that the internal usable width after removing the rails is approximately the same width as the housing, i.e. around 312 mm.

However, it should be noted that this is an assumption, as the exact width of the rails is not specified. In practice, there may be slight deviations, but in general the usable width remains at around 312 mm.