Sorry, as best I know, the FSM doesn't provide that sort of info, and apparently no one knows offhand

I'm going to be installing new rotors and pads sometimes in the next few weeks. When I do, I'll head to Home Depot and get the thread measurements. I would love to get replacement screws for the lock nut myself...you know, something not softt Philips screws
Post back if you find out in the meantime though!