You would need at least 1/2 rod to Drill and tap any 8mm hole.
8mmx1.25 is standard and should be drilled with 17/64th t0 7mm drill. If doing by hand I recommend the 17/64th. for an 8mmx1 thread you would use a j drill - 9/32nd. You might be able to take it to a local machine shop and they can help. They also would be able to tell you what pitch you have. and maybe drill and tap it for you for a small fee since it is only a couple of holes. Good luck.