"The CyberPower CP2RAIL02 4-post rackmount rail kit provides a mounting solution for select 2U and 3U UPS systems weighing up to 500 pounds. The two adjustable rails (right and left) can be expanded from 20.1"" to 35.8"" for various sizing requirements and installed by a single person.4-Post MountingSecures equipment at both the front and back of the rack.Single-Person InstallationSupports single-person installation by inserting half-thread screws into square holes on rear side for temporary support of rails.Adjustable RailsExtends from 20.1” to 35.8” for proper fit with various sizing requirements.Slide-Out Rail StopAllows equipment to slide out a safe distance from the rack before locking in place."