NEC Express5800 User Manual page 347

Installation
Insert the CPU duct cover straight into the chassis while making sure that the CPU duct cover does
not contact with any cables or components on mother board. Adjust the CPU duct cover until the tab
on the right end of the duct cover is engaged with the slot on the chassis.
NOTE:
is surely locked.
Make sure that the tab on the right end of the CPU duct cover
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