Dell Force10 S4820T System Getting Started Manual page 24

Four-post Threaded Configuration:
1 For this configuration, you must remove the flange ear castings from each
end of the ReadyRails assemblies. Use a Torx driver to remove the two
screws from each flange ear and remove each casting. Refer to Figure 1-8,
item 1. Retain the castings for future rack requirements.
2 For each rail, attach the front and rear flanges to the post flanges with two
user-supplied screws at each end. Refer to Figure 1-8, item 2.
Figure 1-8. Four-post Threaded Configuration
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Installation