Hub for Heavy Duty Filament Spool - parameterised

I'm using the excellent "Heavy duty printable filalment spool" http://www.thingiverse.com/thing:10219
and was using the elegantly designed "Ultimaker mount for Heavy Duty Spool" http://www.thingiverse.com/thing:33461
but wanted something more rugged.
There seems to be a general reluctance to drill holes in the frame of Ultimakers, but I have no such inhibitions which freed me to design this simple hub
There is not much room on the inside of the Ultimaker to accommodate nuts, but there is enough. One of the photos shows the nuts on the inside, and another shows the corresonding mounting dimensions for the upper mounting bolt
Although this unit was designed for my Ultimaker it may well suit several other 3D printers.
I've uploaded two stl files for the cap. I'm using 'MG cap plus 0_50.stl' but if this is a bit tight on the threads try 'MG cap plus 1_00.stl' (or scale up slightly in your slicer software).
I've also uploaded the OpenSCAD file which is pretty much fully parameterised for those who'd like to make other changes.