Another +1 for 25.4mm. Here in South Africa I have scoured for the perfect 25.00mm and found the aluminium to be a rattle fit and the stainless steel I ended up purchasing being too tight for the middle assembly causing the bearings to deflect, and having to force into the leg mounts. The Galv mild steel was also 25.4mm.
I have finished printing all the parts and had issues with the PLA’s strength especially the leg mounts where the 4mm bolts went through. Not sure if that was an issue with my machine or not, but the holes promptly broke out with the nylock nuts, so have changed to non nylock nuts which look to be closer to your size of nylock nut. Our Nylock nuts are much narrower than yours. Will apply thread lock liquid on final assembly if required.
I have now changed over to PLA+ which is supposed to be closer to ABS in strength but still prints like PLA. I did all the middle (XY & XYZ) components and initially they look as if the PLA+ does what it claims to do. Dimensional accuracy is spot on, and it seems to even print smoother, less clogs than with the PLA (The 2 x 15 hours for the XY components had me anxious, but not a hick-up)
I would also like to +1 for the Makita 0700 router mount as the Dewalt 660 is not available here but the Makita is a reasonable price.
As I have assembled the parts, I have to compliment you on your thoroughness of design, little features like building in the washers for the bearing holes etc. Very clever and well thought out making assembly easy.
Well done on your design and your generosity in sharing it with the world, I am going to play around with an 8.2mm drill bit for the bearing bolt holes to see if I can salvage the parts, and if that does not work, will wait for V2 25,4mm with baited breathe.