Dell EMC PowerStore 500T Installation And Service Manual page 16

Figure 7. Installing the NVMe expansion enclosure rails (rear)
Figure 8. Installing the NVMe expansion enclosure rails (front)
5. Add the retaining screws that came with the rails to the front and back of both rails.
NOTE: Use the washers that came with the rails if the rack holes are square.
NOTE: The screw hole at the front of the rail is behind the rail clamp.
NOTE: You will need a long handled screwdriver to reach the screw hole at the rear of the rack.
16 Install a new base enclosure and optional expansion enclosure