The studs measure 11.3mm. StewMac recommended an 11mm hole so I drilled a test hole at that and also a 7/16” one as well. The 11mm felt snug, the 7/16 a tiny bit loose so I decided to go with the 11mm. In hindsight I think I should have gone with the 7/16 and given them a little titebond for good measure.
Chalk it up to inexperience. Perhaps modifying the kit to take a different bridge was a step too far on my second kit. I have to work this morning but I’m itching to have a go at refitting them.