Parametric Filament spool holder

I liked the previous versions of this ( http://www.thingiverse.com/thing:12868 and http://www.thingiverse.com/thing:13643 ), but I have Bosch Rexroth profiles ( http://uk.rs-online.com/web/c/workshop-site-equipment/steel-tube-aluminium-structural/bosch-basic-mechanical-elements/ ) and wanted something that didn't flex when tightened. Also I have impure thoughts about the OpenSCAD minkowski() function...