The one for the wire covers is 4mm. The ignition coils is 5mm.Very easy! Very accessible. You'll need a hex-bit for the ratchet to get the bolts that hold the coils down and to remove the black wire covers. Sorry, I don't remember the size.
The job is a real joy compared to the BMW 12-cyl. If I could get that done in an hour, I was thrilled. The Maserati engine is very accessible.