It would help if more dimensions are mentioned in various places. I had to puzzle out the approximate sizes of the aluminum channels, and the only dimension for the Microrax dual nut plates is 3mm (they don’t look one-dimensional).
You had to puzzle out the size of the channels… You mean the ones that have the length right there in the part number. 
Yeah the ASB-506 is listed as “Aluminum Channel - 6” Single Pack" right there on the website. They are 1" x 1" on the other dimensions. And of course there are always the 3D drawings listed here.
lynxmotion.com/s-5-ses-3d-models.aspx
The nut plate shares the same spacing as the brackets. That being 10mm. The 3mm refers to the screw that fits it. I’ve not been asked for the dims of the nut plate before. 