ICY BOX IB-129SSK-B is a mobile rack for 3.5"/2.5" SATA/SAS HDDs that can be installed in a standard 5.25" bay. It supports hot-swapping, has a key lock to prevent improper operation, and features an efficient passive cooling system to ensure silent and stable operations without a fan. With its compact design, aluminum construction for better heat dissipation, and support for various HDD sizes and interfaces, it's a versatile solution for expanding storage capacity and managing multiple drives in a computer system.