I was having some RC parts machined and was needing to find out the dimensions for an M3 screw to be counter sunk. I was wandering what the diameter would need to be along with the depth required for the screw to sit flush? I am not an engineer or machinist, but did some research online and found some different info. Based on what I found I was thinking:
diameter =6.72
depth = 1.86

Mickey you need a metric countersink (90 degree). They have combo countersinks that drill and countersink the hole. Or you can buy the drill and countersink separately. Metric flathead screws have a 90 degree angle and SAE screws have a 82 degree angle. The countersink bevels the hole so a flathead screw will fit flush.

PS in case you didn't know M3 is a metric screw (M=metric).

Here is a link to a combo countersink to give you an idea of what it looks like.
http://www.mcmaster.com/#countersinks/=qjl36q

5.9-6.0mm wide
2.3/4mm deep.

Spot on! The only thing I could add is to source your hardware FIRST.Not all is the same EXACT dimensions.The ideal finished depth/diameter of the countersunk hole will depend on the hardware.I have sourced hardware and found variances between lots from the same supplier that required a little tweak to my countersink operation to make things perfectly flush.