mairomaster , 10-18-2016, 01:55 AM
I forgot to mention that you also need a keep-out shape, so that polygon pours and other copper won't get into the area - otherwise your risk the screw head to damage something. The easiest way to achieve this is to create the arc on the top layer, to define it as a keep-out (from properties) and to set a solder mask expansion (could be from rules).
However, in general that is not a very good approach in my opinion. I create my mounting holes the same way as Robert - using simple TH pads with a pad diameter big enough for the screw head. Apart from no need to worry about keep-outs, there is a copper surface below the screw head which in theory makes the mounting hole a bit more durable. It also looks better in my opinion and it is the most common method of creating mounting holes.