HP 98568A Installation Instruction page 29

HP 98568A Backplane Expander
9. Locate the two sliding clips on the top of the slotted cover and press them
toward each other as far as they will go.
Figure 2-3.
Sliding Clips
10. Place the slotted cover upside-down on the bottom of the expander, with
the front of the cover toward the front of the expander. The slot in the
cover should line up with the slot in the expander.
Adding Expanders 2-5