The extrusions are available as one slot, two slot, three slot or slotted on all 4 sides. I used 1 1/2' square from Futura Industries. The extrusions can be purchased 1' square, 1 1/2' square or in metric dimensions. Hand tools, a wood cutting (3450 rpm) chop saw and a drill press are the only shop tools required.
Welding or woodworking skills are not required. The extrusions are cut to length and then bolted together. One method of building structures inside a Sprinter is to use 80/20 ( or Futura Industries ( or other brands of aluminum extrusions.
