I've never done this on a roasted neck, in fact the roasted maple neck for my current build is currently in Cagey's capable hands. What I do, using knowledge I also acquired from Kevin, and using type 400 inserts, is use a 1/4" forstner bit to drill the holes, and then thread them with the 5/16"-16 tap. (Note that the external thread on type 400 inserts is 5/16"-16 instead of 5/16"-18.) This ensures a snug fit, and also makes up for the fact that the barrel of the insert is 1/4" by expanding the hole to fit the threads. In normal maple, the threads will generally drive firmly into the threaded holes, but as I said, I've never done this on roasted.....