Draft Document – Gully tops and manhole tops for vehicular and pedestrian areas – Securing of the covers and the gratings within the frame
standard by Deutsches Institut Fur Normung E.V. (German National Standard), 06/01/2006

Draft Document – Gully tops and manhole tops for vehicular and pedestrian areas – Mass per unit area and pull-out force
standard by Deutsches Institut Fur Normung E.V. (German National Standard), 05/01/2013