Mellanox Technologies Grid Director 4036E Installation Manual page 38

Use the lower holes in the short bracket as shown in the figure.
Important: At this stage, do not fully tighten the screws.
17. Adjust the short brackets snuggly onto the rack's vertical rail using the adjusting holes
(make sure that the rail is perfectly aligned by using the same U as used in the front of the
rack).
18. Tighten the rack screws (rack screws are not supplied).
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Hardware Installation