Here are the photos of the brass-to-RC rail connector , Marco. Click on them to make them bigger.
First, a photo showing the side of the connector which fits to the brass rail and then one of the RC rail side of the connector.
Next, the connector and the two types of rail ready to be joined together. As you can see, the fishplate on the brass rail has to be removed.
A photo of the brass rail with the connector fitted. The rail needs to be flush with the connector; pushing the two together does this, or you can pull the brass rail back until it is flush. The latter may be the easier way.