The Depth Gauge for Silentia can be used to VERIFY the correct drilling depth for the 700 Series Silentia Hinges (13.5mm). A simple hand-held gauge with pre-set 13.5mm depth, 35mm in diameter. If the top surface of gauge rests either flush or below the door surface, (check by running your finger over the edge of the hole with the tool inserted) the door has been drilled deep enough.