New Design The new Flexing Rail System incorporates multiple new design features which enhance the simplicity, structural integrity, and functionality of the rails. This set of rails requires your headboard and footboard in order to support your bed. Simplicity Each rail is formed from one piece of 4" wide carbon steel. Foundation and mattress sit on a 2" wide internal horizontal flange on each side rail. No slats are needed. There are no rivets nor attached items used in the manufacturer of each rail. Structural Integrity The hook plates on each end of the rails are equipped with "Tension Fingers" which flex to provide the snuggest and most secure fit with the headboard and footboard. No rivets are present in the hook plates which could loosen over time. Center Support Included The included 2-Leg Cross Support provides center support for the the foundation unit and mattress. Center support is uncommon for twin / full size beds. The cross support hooks into the side rails from the underside in a recessed slot in the side rail.The flat supporting surface of the side rails for the bedding is not compromised. Adjustable Legs The two legs on the center support can adjust from 8" to 18", with the upper heights being achieved with the included extension pieces. The adjustable legs enable the rail set to adapt to uneven floors and various height headboards and footboards. A center support can enhance the length of service of the mattress and foundation unit by reducing torsional flexing of the foundation unit and mattress.