Hi
I'm 95% sure its M3
My advice would be to do what I did. Go to a place that specializes in screws nut bolts etc. Take your guitar with you and try an M3 or maybe a 2.5.
Buy a few and keep them as spares.
Having said that, I super glued one into the slot, got exactly the right tension on the trem and then left it to dry. Never had a problem with it since. The trem goes in firmly with no excess play.
I hope that's helpful
Mark