Document FR-A-2 765 256 describes a universal cover for a manhole for connecting chambers. 
The cover comprises a base body that includes several attachment protrusions to which it is possible to fasten functional elements, such as hooks or a lock so as to form either a slave cover or a master cover. 
Each attachment protrusion comprises surfaces for applying functional elements that are inclined towards each other.  The functional elements have surfaces inclined in a manner complementary to those of the attachment protrusions.  The functional elements must therefore be made specially for the cover and as a result are costly. 
Furthermore, the functional elements are fastened by screws on the attachment protrusions.  This fastening means is costly in terms of assembly time and logistics because a large number of components must be stored.  Moreover, the screws can be released in an untimely manner. 
Also, the functional elements are fastened on attachment protrusions that are not useful when no functional element is attached thereto.  The cover is therefore costly in terms of material.