My McWire cartesian robot: Part 1

I will be following the instructions on this link http://www.reprap.org/bin/view/Main/McWire_Cartesian_Bot_1_2 to build the McWire cartesian robot for my RepStrap machine.
Here are my plumbing parts. The aluminum is next, if we could just get proper specs of the stuff. The U rail to be specific. All the site says is 3/4" x 3/4"... the link in the reprap parts lister is old & that product is no longer stocked by the supplier.
& here it is, rather easy to assemble. I wish they would list the measurements in metric & not just in the imperial system, that would make life easier as well.
After all, the goal of reprap is to make it easy for anyone anywhere in the world to assemble!