For this build, the NUCs get screwed onto their trays from the bottom with M3 screws. From there, they are slotted into their individual frames. The two spacers go between the three frames, and the mounts go on each end. The rods holding all these separate pieces together are two M5 x 500mm rods I ordered on Amazon. They were a little too long for the rack, so I ended up using a hack saw to trim them down. I would recommend printing the frames and mounts with support, and definitely printing the mounts with a higher infill percentage so they can be as solid as possible.