Originally Posted by ...Well, it gives me time to check my tap-n-die set and make sure I have M5x0.8mm, and [u
also figure out what size pilot drilled is used before tapping[/u].
Tap drill sizes for metric threads are the major diameter minus the pitch. In your case, 4.2mm (0.1653") ~ #19 drill. 11/64" would also work (0.1719" dia), with slightly looser threads, but shouldn't be an issue since you're just holding the guide in place.