Outside rails are constructed of extruded aluminum, to provide strong, but lightweight storage solution.
Outside rails are designed with slots to hold a 2x4. This helps protect the material being stored as well as the rail surface.
Outside rails have 1" diameter round holes spaced every 3". A secondary plate with identical holes is located below the top of the rail, 1" from the bottom.
Rails are 6" wide x 3" high x 60" long and can butt together for desired length.