Some screws have no thread up near the head.
I've never given this much thought until recently when I realised that
if you're fastening a sufficiently thin skin (sufficient meaning less
thick than the clear shank length) to the timbers below then you get the
same effect as drilling a clearance hole in the skin and putting a screw
through, namely that the skin is pulled in nice and tight.
Is the intended function of the design, and does anyone know of a
supplier of such screws in something like 50mm with a 20mm clear part,
which would be ideal for fastening flooring chipboard nice and snuggly?