The 4POSTRAILKITHD is an adjustable rack-mount shelf system that 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 select rack-mount UPS systems or other heavy pieces of networking or power protection equipment with a 17.5-inch-wide rectangular chassis. A pair of expandable "L brackets" adjust to any setting between 20.5 and 36 inches. The kit includes mounting hardware compatible with square-hole racks. Supports up to 500 pounds (226.8 kilograms)