The 4POSTRAILSM 4-Post Rack-Mount Installation Kit supports heavy UPS systems in your EIA-standard four-post rack. The two L brackets mount to the outside edges of the rack's vertical mounting rails - the edges facing the side panels - using the rails' square mounting holes. Attaching the 4POSTRAILSM to the side leaves your front and rear mounting holes free for equipment.The brackets support up to 250 pounds and are compatible with four-post racks with a mounting depth of 16.5 to 21.5 inches. In addition to UPS systems, the 4POSTRAILSM is compatible with other heavy networking or power protection equipment with a rectangular chassis of 17.5 inches in width. Rack-attachment hardware for square-hole mounting is included.