| # | Country | Total Patents | |
|---|---|---|---|
| #1 | Netherlands | 5 | |
| #2 | EPO (European Patent Office) | 3 | |
| #3 | Denmark | 2 | |
| #4 | United Kingdom | 2 | |
| #5 | Austria | 1 | |
| #6 | Switzerland | 1 | |
| #7 | Germany | 1 | |
| #8 | Spain | 1 | |
| #9 | Italy | 1 | |
| #10 | Sweden | 1 |
| # | Industry | |
|---|---|---|
| #1 | Civil engineering | |
| #2 | Mechanical elements |
| # | Technology | |
|---|---|---|
| #1 | Foundations and excavations | |
| #2 | Sewers | |
| #3 | Pipes |
| # | Name | Total Patents |
|---|---|---|
| #1 | Raatjes Egbertus Sijbolt | 6 |
| #2 | Raatjes Egbert Sijbolt | 2 |
| #3 | Raatjes E S | 1 |
| Publication | Filing date | Title |
|---|---|---|
| NL8402712A | Manhole cover for road - has adjustable screwed support ring with pressure pad thrust outwards by radial forcing screws | |
| NL8002125A | Kolk with improved possibility for fast cleaning. | |
| EP0009835A1 | A cover such as from metal, for a traffic road surface | |
| NL7905854A | Cover. | |
| NL7701246A | Cover of an opening in a road. | |
| GB1116951A | Spigot and socket joints |