The housing consists of 3 parts:
The case itself is designed to push the card in until it snaps into place by itself.
A second small part (labeled "C64") makes sure that the card is locked in this position.
The third longish part (labeled "LIGHT AND DARK") is a cover for the upper part of the case. This part has a purely optical function (it covers the gap in the case) and is actually not necessary for the case to work.