Connecting the hemispheres

There isn't any room for normal M20 bolts to connect the hemispheres. To fix this I made 4 of these:

The lower side has M20 thread, the upper half is split in 4 and has M7 thread inside, the bolt has M7x1 at the tip but for the rest it's M8x1.
When the upper hemisphere is placed over them, fastening the M8 bolts will widen the 4 segments and position the upper hemisphere.