Two 11", 14", or 17" center support legs and 8 wood screws. 
Use the 11" center legs with the 12" optional leg height.  Use the 14" center legs for the standard 15" platform height.  Use the 17" center legs with the 18" optional leg height.
 
These legs can be used to lend extra support to the outside rails of all sizes and/or the middle rails of the full and queen sizes of the Nomad, Charleston, or Lexington platform beds. Please note that the king size Nomad comes with this set of center support legs for the middle two rails.  These support legs are only needed if you plan to exceed the 600 pound weight limit of the Nomad, Charleston or Lexington bed frames.