EMVANV Stainless Steel Hard Drive Cage, 5.25" to 5x 3.5" with Fan Space, Adapter Rack Bracket (Silver)
When you’re trying to maximize drive capacity, a 5.25" to 3.5" cage can be a really clean way to add more disks. This style of bracket helps turn front bays into usable storage real estate, which is exactly what a NAS build needs. Just make sure you plan airflow along with density.
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