"Fredxx" wrote in message
...

Common UK parlance for a bolt and a set screw is that there is thread the
entire length of the set screw, whereas a bolt is only partly threaded.

Anything else is contrary to UK convention, for decades, perhaps rather
than centuries.

You are of course perfectly free to believe otherwise, but is a foolish
approach and most unhelpful in making purchases in the UK of, or
specifying in the UK, machine/set screws / bolts.

So the bolts (and corresponding nuts) that I bought the other day were not
really bolts but screws because they are threaded right up to the head.

I imagine that the nature of the head is also a factor in the screw/bolt
decision. If it has round head with a flat or cross-head notch, tightened
with a screwdriver, it's a screw; if it has a hexagonal or square head, it
may be a bolt depending on how far up the shank the threads continue.

There is a third category - the ******* bolt from hell! The spare wheel on
my Peugeot 306 was held into a cage under the boot by a bolt-sized screw
with a *round* head that had a semi-cylindrical notch in it (ie the sides
were not vertical). You were supposed to use the flattened end of the
wheelbrace as a crude screwdriver. This idea failed fairly spectacularly if
the captive nut on the cage got seized onto the threads (it was exposed to
all the water that was thrown on the underside of the car), because the
curved sides of the notch in the screw head meant that the "screwdriver" end
of the wheelbrace just climbed out of the notch. It took an RAC man about
half an hour to free the seized thread with WD40, heat, lots of cursing and
imprecations about the parentage of the person who had designed it. How much
more effort does it take to cut (or die-stamp) a semi-cylindrical notch than
to cut one with vertical sides using a milling machine? Or to mill/die-stamp
a proper hexagonal head the same size as the wheel bolts.