Post by Jack Campin Post by Julian Bradfield
While fixing the stair door today, I found that the door closer had
been (inadequately) fastened to the frame using a type of screw that
I've never seen before (and very poorly chosen for wood).
The screw is a straight cylinder, with a fairly low profile thread
(bit more than a bolt, but less than a wood screw thread); it has a
partly smooth shank; but most unusually, part of the tip is also
unthreaded, and the tip is formed in a precise sharp conical
point. The unthreaded tip portion comprises the point and about 1.5mm
of cylindrical shank before the point.
What is it?
Sounds like the sort of thing IKEA uses in MDF.
It might be a kind of self-tapper where the unthreaded part is either
used to guide the screw into a pilot hole before the thread bites or, if
the end is sharp enough, it acts as its own bradawl and drills its own
pilot hole. There's a selection similar things among these:
ISTR also seeing machine screws (bolts, set screws, grub screws) with an
unthreaded start. I think it's for guiding the screw into the hole
where access is difficult. See the first image and look for 'dog point'
The University of Edinburgh is a charitable body, registered in
Scotland, with registration number SC005336.