The 4POSTRAILKIT adjustable rack-mount shelf system supports heavy UPS systems in 4-post rack-mount applications. Includes one pair of expandable "L bracket" mounting rails to offer front-to-rear support of rack-mount UPS systems. Pair of expandable "L brackets" adjust to any setting between 20.5 and 36 inches. Includes mounting hardware compatible with square-hole racks. Set of temporary placement pegs enables simple single-person installation by allowing the rails to be held in place while attachment hardware is installed. Also compatible with other heavy pieces of networking or power protection equipment with 17.5-inch-wide rectangular chassis. Supports up to 250 pounds (113.4 kilograms).