I am not sure what the 19.35mm you are referring to. The hole patterns for mounting the carriage measure 20mm when I look at the .STL files in a CAD program. That is the only 20mm I can think you are referring to. I also came up with a better nuttrap for the rod screws, but have not finalized that design yet. I took a quick look at making the sliders work for M6 & looks like it should be easy to do. I used 10mm countersunk holes for the M5 Philips flat screws I am using. I do not have any M6 screws to check but from http://www.spaenaur.com/pdf/sectionR/R11.pdf , M6 heads are 11mm & would have to make that hole at least11.5mm for clearance. Without changing the outside profile design that would probably make the walls a little too thin. Changing the profile should be fairly easy to do though, so I will look at closer this weekend. There is also a newer version of this design locaded: http://www.thingiverse.com/thing:1793640 & that will be the one I update.