Clearance hole for DIN 7991 metric flat head screw, does it have radius under head?

Hi,

I'm using M3 metric flat head countersink screws, DIN 7991. The max theoretical sharp edge diameter of the head is supposed be be somewhere around 6.4-6.8mm. I've made my countersink 7.2mm at 90 degrees but I still get some screws sticking out of the surface by about 0.05mm. I have the hole at exactly 3mm for a close fit, but I was wondering if the underside of the head has a "fillet transition diameter", and the radius is hitting the edge of the 3mm hole, pushing up the screw?

I've tried looking around but can't find information about the radius. Looking at the screw, it's hard to see because the threads are so small, but it appears the sloped surface under the head starts from the minor diameter of the head, so any radius should be cleared within a 3mm hole?

Or would it be better to use a 3.4mm, or 3.6mm hole?

Thanks

Yeah, that is always a problem.
And yeah, it could be the transition region blocking you.
One solution for that which does work fine is to counterbore the transition region to, say, 4 mm for 1 mm depth. Then you can keep your standard 3.0 mm hole.

However, I have seen some countersink heads with a variable height. If you look closely at the rim of the head you may see different thicknesses there, anywhere from 0.1 mm to 1.0 mm at least. That can be a real pain.
In this case you have to push the countersink in by another, say, 0.5 mm depth. That may result in most screw heads being below the surface, but I have never see that as a problem.

Cheers
Roger