A trackball assembly, with 1" ball. Trackballs this size are industrial and cost like $300, so I thought I'd try making one with off the shelf parts, and this 3d printed assembly. It cost a lot less than I thought, and I hardly did any hollowing out.
***** Update: It looks very nice in black detail. Production quality, even. The spherical mesh in the middle broke a little, so I'll have to shore it up a bit in the revision. Currently awaiting the parts to assemble it.