IBM NeXtScale System Planning And Implementation Manual page 147

Six 1U vertical mounting brackets in the rear post flanges, which can be used
for power distribution units, switches, or other 1U devices, as shown in
Figure 5-8.
Cable
openings
Figure 5-8 1U Power distribution unit mounted in 1U pocket on flange of rear post
M6 clip nuts
Chapter 5. Rack planning
129