Bryan,
The holes are cut into a .25 piece of ABS plastic with a $100,000.00 CNC milling machine. That holds a tolerance of + or - .0002. The covers are .187 FF type UV grade plastic, and the whole thing is held together with 14 nylon barrel screws. I tried circle cutters in drill presses, table routers with a pattern, and really big drill bits but nothing beats modern technology.