I'm actually not sure why the 'spine's are there. The spines are mainly for appearance and they do not have any particular mechanical significance. On a PCB they appear as silkscreen only. The overall diameter defined by the tips of the spines is usually much smaller than the diameter of any screw head or washer or across the flats of a nut of a size suitable for passing through a hole dimensioned as a clearance hole. Here's a picture of what this footprint looks like for a 3.5mm hole (i.e. an M3 clearance hole): ![enter image description here][1] [1]: /editor/20161022/580a6c882f2f4.jpg

@andyfierman Great, thanks a lot Andy