Apple Power Macintosh 5400 series - Manual (Page 153)

9 Insert the adapter into the PCI slot on the main logic board. Make sure the metal fence on
the PCI card engages the hook on the vertical plate and that any connectors on the card
protrude through the PCI access port opening.
Don’t force the adapter. If you meet resistance, pull the adapter out and try
again. To see if the adapter is properly connected, lift it gently. If it resists and
stays in place, it’s connected.
The PCI card is properly seated when the card’s metal
“fence” engages this hook on the vertical plate.
Vertical plate
Card fence
141 Installing Expansion Cards and Additional Memory