The SmartRack 45U Standard-Depth 4-Post Premium Open Frame Rack has no doors and no side panels. The 'EXP' version is an expansion model used when several cabinets are bayed together. Its integrated baying tabs make it easy to combine multiple enclosures in rows for data center applications. This enclosure is also compatible with hot-aisle / cold-aisle configurations. The SR45UBEXPND houses 3,500 lb (1588 kg) of standard 19" rack equipment in 45U. Its front and rear pairs of vertical rails have square mounting holes that are adjustable in quarter-inches increments from 4 to 37". Adjustment is quick and an easy-view depth index ensures consistent rail placement without requiring time-consuming measurements. Each rack space within the enclosure is numbered for ready reference. Two of the adjustable vertical mounting rails support toolless button-mount 0U installation of up to four compatible PDUs and cable managers. This feature makes it easier to route cabling to rack equipment and reduces cord clutter. All components of the SR45UBEXPND are grounded to the enclosure frame. Front and rear threaded grounding points are provided for connection to the facility earth ground. To simplify deployment, the SR45UBEXPND comes with preinstalled casters that enable it to be easily maneuvered into the desired location, where it can be secured by adjusting the preinstalled levelers. Note: The casters are intended for minor position adjustments and are not designed for moving the enclosure over long distances.