Apple Mac Performa 5300CD - Manual (Page 116)

3 Align the card over the communication slot.
The communication slot is the rightmost slot on the logic board as you face
the vertical plate.
4 Press down on the card until the connector is solidly in place.
Don’t force the card. If you meet resistance, pull the card out and try again.
To see if the card is properly connected, lift it gently. If it resists and stays in
place, it’s connected.
Communication slot
Vertical plate
Communication
card access hole
106 Appendix B