Centers the hole in the rod, so the endcap is centered when assembled.
Slightly increases the hole size, to avoid breaking the end cap while trying to force it in. (Edited to add: My particular printer/filament combo may have needed a larger hole here than others. Still figuring out the right horizontal-expansion settings for me. If it doesn't fit snugly, use a tiny bit of super glue.)
Scales the ring down slightly as suggested by some commenters on the original design.
Printing notes:
0.2mm layer height
I printed the cap with 1.2mm thick walls, top, and bottom
Your usual settings for standard quality should work well
cdzombak
