Apple Performa 6400/180 - Manual (Page 190)

Upgrades Communications Card - 19
2 Align the card over the
communications slot.
3 Check the external
connector on your card
to see if it has a hook.
If the communications
card has a hook, be sure
the hook engages the
metal on the inside of the
logic board fence. Push
down on the back end of
the card until it is
firmly seated in the slot.
Communication Slot
Logic Board Fence
Communication Card
Hook