(Photo: Örjan Stål)
I found the above photo in a publication from the Stockholm traffic and park administration (Trafikontoret). That in turn led me to a helpful person who told me that the above were the standard grates in the city of Stockholm up to the 1990:s. He also was kind enough to supply me with a plan of such a grate.
Since I did not want to manually cut all those tiny holes, and get them all straight and tidy at the same time, I decided to instead do a 3D print of a grate. Such a print is now awaiting processing at Shapeways. Here is what the model look like. It consists of four different parts, that will be cut apart and fitted into a frame I will build from styrene.