"NY" wrote in message ...

I would say the the difference between a bolt and a machine screw is much less (both
have parallel threads) than between a machine screw and a tapered wood screw. If you
want to be imprecise, calling a machine screw a bolt is less confusing than calling it
a screw which is more usually tapered.

But a machine screw like all screws, is screwed into a female thread.
Either one already existing in the case of metal screws or one made
in the course or operation in the case of wood.
Thats why they're called screws because they have to be screwed in.
Whereas a bolt is simply inserted into the hole. And it's the nut
that has to be screwed onto the threaded end of the bolt.



BTW you seemed to have overlooked my rather unfortunate error in
saying that studs are threaded into cylinder heads; rather than
what I should have said, threaded into cylinder blocks.

Likewise, "wheel bolts" (for fastening car wheels onto hubs) are really (very large)
"machine screws" because they screw into threads in the hub rather that into nuts on
the reverse of non-threaded holes in the hub.

As a matter of interest, when and why did cars change from using threaded studs
fastened into the hub with the wheel fastened to the hub by nuts, to the modern
practice of using bolts (machine screws?) into threaded holes in the hub?

No they're definitely screws, of some kind or other if they have to be
screwed in. Maybe calling them all "bolts" as with cylinder head "bolts"
is some kind of affectation among car mechanics.

Or maybe all screws over a certain diameter are referred to as "bolts"
regardless. I would be more than willing to defer to any reputable
source claiming that this was indeed the case.

All My Oxford Dictionary source says on the subject is
3 A stout pin for fastening; a door-fastening comprising a sliding bar and
a socket on a jamb, lintel, or threshold; a metal pin with a head for holding
things together, usu. secured with a nut or riveted. ME.

So no reference to size, but a "usu."



Was it to make it easier to fit the wheel, in that you only have to locate the centre
of the wheel onto the protruding boss on the hub and can then rotate it until the holes
line up, rather than having to locate four (or more) holes in the wheel onto the
protruding studs? My impression is that all manufacturers seemed to change over at
about the same time, some time in the late 1970s or early 1980s, which suggests some
external factor that caused them all to change.



michael adams

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