Back in May, the technician that fabricated the first prototype suggested that the grub screw length should be flush with the face so that it's more visibly obvious when the grub is fully tightened or not. Thus, I've added some 4mm trenches so that the actual length of the screw+ball bearing stoppers are the same everywhere.

I've also had to reduce the depth of the heatbreak threads to prevent the topmost grub void from creating holes in the mating face. I've ensured there's at least 1mm of wall thickness.

Using a 2mm ball, and a 4mm grub screw, the top of the screw should be just-about below the surface. It might be better to use a 2.5mm bearing to be even closer to the exact length.