NEC Express 5800/320Lc - Manual (Page 336)

System Upgrade 8-35
7. Align the terminal segment of the board with the connection of the slot and insert the
board slowly into the slot.
TIPS: Check to see if the edge of the bracket (taper) is inserted into a slot of the chassis.
In the case of a long board, check also to see if its other edge is inserted into the bracket
guide.
Slots for inserting
bracket edges
Guide