Name that screw

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.

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? 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.

In the UK it would be a bolt. In other countries it may be a screw.

This link may help to understand the USA vs UK nomenclature:

Another example of this kind of distortion:

Be careful as wiki is very much USA centric.

For the UK, it's simple. A bolt is a fastener with a portion left unthreaded. A machine screw, or set screw is fully threaded.

If you ask a UK supplier for a bolt you will get a partly threaded 'bolt'. If you ask for a machine screw or anything with "screw" in its name, it will fully threaded.

YMMV + I am sure there are exceptions! :-)

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.

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

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

michael adams

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My astra wheel nuts /bolts are not screws.

If you've got nuts, then they're bolts obviously.

That's the definition of a bolt; something with a thread on the end onto which is screwed a nut.

The OP is talking about screws which you screw into the hub with no nuts involved.

michael adams

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So you're saying that standard pattern woodscrews, all of which have a plain shank are actually bolts then ?

" ?

As on the cylinder heads as found on the engines of Mail Coaches and similar you mean ?

You probably have at some time or another but I'll let that one go for now,

So yes, go on, do your lap of honour.

michael adams

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I called it a screw as it is fully threaded not part threaded like a bolt. There is no taper or shoulder

Well a new one on me ... never heard of wafer head screws .... but that is what it looks like .... Thnx

Now have to find one.

too thick ....... My solution (it seems) is a "flanged button head screw."

It is not a Pan Head (or cheese head screw)

Then that would be a Hex head machine screw, not a bolt.

You can use a machine screw as a bolt providing it goes right through and you can thread a nut on the end and tighten it that way. Depending on how oversize you make the hole you can either thread the screw through the hole or push it through, like any other bolt.

michael adams

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Different trade where different terms are used. Sheesh.

The last mail coach I saw ran on rails. You're now being ridiculous.

I don't feel any need. I just don't see your point.

They aren't bolts, they are machine screws.

Bill

Both coach bolts and coach screws have a plain shank and both are used in the one trade.

Which was coachbuilding presumably, in the first instance..

Trains don't have cylinder heads. I'm just wondering where these bolts were to be found centuries ago. Obviously if they'd been on Mail Coaches they'd have been coach bolts, but then they might also have used coach screws on Mail Coaches as well.

With a bolt Its possible use a slightly smaller diameter providing the head and nut are large enough; whereas with a screw, the thread needs to exactly match that of the hole.

michael adams

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I defer to your greater knowledge, of course, but I have never heard studs called bolts. In fact, the humble stud contains in its person both what you call a screw and what you call a bolt. So best to call them studs?

I'd just add that most common M4 screws have a 0.7mm pitch, and this one looks to me quite coarse. But 0.5mm (and possibly other pitches) also exist. So I'd check it, if not with a thread gauge at least with an M4 nut which if general purpose will probably be 0.7mm.

Ok. Woodworking techniques were also used in steel/iron structure. If you look at the bridge at Ironbridge you'll see all manner of woodworking techniques that are of course now obsolete.

Some do, mainly diesels and not sure how Deltics are configured.

There is a rule of thumb that a thread should penetrate 1.5 x major diameter. Everything has a tolerance.

The US has difference tolerance for screws and bolts.

The ISO/BS standard doesn't distinguish between bolts and screws and just mentions "screw threads" or "coarse threads" and their tolerance. It even has "screws" and "nuts" in the same table.

It was Andrew who called them bolts not me. As in " My astra wheel nuts /bolts are not screws".

This was in response to the OP who was talking about machine screws which are screwed into threaded holes in the hub, with no nuts involved.

Formerly, as the OP explained the wheel was fastened with nuts threaded onto the end of studs as in "As a matter of interest, when and why did cars change from using threaded studs". But neither the OP nor myself ever referred to those studs as bolts

Presumably this was what Andrew was referring to only he chose to call them bolts. And for all I know bolts may in fact have been used on Astras in that situation for some particular reason. Which Andrew having a greater knowledge of Astras than myself, will of course be in a better position to answer.

michael adams

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