A SIMPLE POINT !

If a bolt has thread all the way to the head and is longer than about 1" or 25mm then it is NOT a bolt - it's a set screw ! If there is plain rod between the head and the thread it's a bolt. This simple point may save some one trouble when ordering set screws or bolts. Good luck, Noel.

Set screw? - Machine screw, surely.

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Depends on which school you went to I think ? Set screw is a more descriptive term but the importany think is to get the right part for the job ! Noel.

Set screw is the correct technical term. But unfortunately sloppy definitions mean that set screw can also be used to mean a grub screw. Machine screws imply a non-hexagon head.

It's almost as bad as describing a milling machine as universal just because it has horizontal/vertical capability.

Andrew

Always known them as set screws, but the term machine screw is just as ' correct ' to my knowledge. Either way, distinctly different to a bolt.

regards Mike

I was taught (and it seems logical to me) that a macine screw is the generic term, and so called to distinguish from other types, such as wood screws. A bolt is one subset of machine screws, with plain portion of shank. A set screw is another.

Mostly a difference between US and UK terminology I think.

Rod

Isn't a bolt used in conjunction with a nut (& washer etc.) and a screw (machine, set, grub, shoulder etc.) is fitted to a threaded hole although there will be as many opinions on this as there are types of screws and bolts

Looks like Wiki has it wrong on this topic, not the first error on that platform. !!!!!!

Emgee

Hi, I've always known set screws to be hex head that are fully threaded, a bolt has a plain shank between the head and the thread and the head doesn't have to be a hexagon e.g. coach bolt or even square head bolt, machine screws normally require a screwdriver to tighten them up. of course, all of these can and are used with or without nuts.

Regards Nick.

At the bolt supply company I worked they were called tap bolts.

Hope they were not used in conjunction with tap washers for critical jobs

Only if they were being fitted by the company drip .

In case anyone is wondering what the fuss is about, if loaded in shear a bolt with a plain shank has a much better abutment against a round hole, and has a significantly higher shear load capacity. This implies that the plain bit should be just less in length than the thickness of the 2 bits that it is going through

You may also run into problems if you order a coach screw using Noel's definition of a bolt/screw as this is a coach bolt

And this is a coach screw

Edited By JasonB on 27/08/2021 14:59:31

In the colloquial-speak I'm used to, anything with a round head - machine or wood thread, domed, cheese, flat, c/sk or cap, and slotted,Phillips, Pozi, hex socket, torq or other drive - is a screw.

Anything with a hex head is a bolt, however high or low up the shank the thread goes.

I'm not saying this is right, just that it's common parlance. I've seen enough variations - such as setscrew/grubscrew conflation as above - to think that the only way to be certain to get the right screw is to

• buy from shops, where you can check any important features such as threaded length;
• from suppliers who specify their wares exhaustively;
• or make 'em yerself.

Well, for a start, I differentiate between cap-screws and cap-head bolts. The bolts have a plain section of shank. Screws are made to be screwed all the way in and secure the part on the head - that can be a hex or round. Cap heads are particularly useful when counter-bored below the surface. Bolts are generally tightened with a nut, or threaded into a different member to that which is being secured by the bolt.

I specify dependent on the situation in which the fixings are to be used. There are often alternatives, but also some specific fixings (coach head bolts are one example that are never going to be screwed in!) for some applications.

I don’t think I have ever seen a coach bolt/screw threaded completely to the head.

In summary, all is not simple when specifying a fixing. There are always going to be exceptions to the basic ‘rules’. Some bolts even have square heads, after all.🙂

Well, that's cleared that up then!

Nothing in life is simple, is it ?