4 replies to this topic

[mvahora]

Not sure if this has been asked before

What is the difference between a bolt and nut vs a setscrew when the bolt and nut has the thread also up to the head.

I was after 5/16 x 3/4 unf ht grade 5 setscrews for radius arm brackets amongst other areas on the mini.

Phoned a recognised fastners supplier who said they had the setscrews but when i went to collect the box said bolt and nut on them? Also theyre in black zinc or black plated not sure exactly.

Bit confused.

Edited by mvahora, 12 November 2024 - 02:53 AM.

[Spider]

A Bolt has around 1" of thread and then the rest of the shank to the head is plain on the nominal diameter of the fastener.

A Setscrew is threaded all the way to the head.

 

So, bolts 1" and under will all be Set Screws, though, ordering them as a bolt will get you the same animal.

 

Steel Fasteners generally come in Black or Zinc or Bright, though sometimes they can also be offered in Plain.

 

Plain is just plain steel. If left without oil or paint, these rust fairly quick.

Black is an oily finish (though not always oily to the touch). It's just minimal corrosion resistance, but over a period of about 6 - 12 months, light rust can usually be seen.

 

Zinc and / or Bright is Zinc Plated, it provides good rusts resistance, though in time, like 5 - 10 years, might start showing rust. Salt and similar chemicals will make these go chalky in appearance and make them rust in much shorter time frame. Most of the original factory fasteners were Zinc Plated.


While a little outside of the original subject, Stainless is often mentioned. Stainless does have it's uses and places but I would caution against using it for just about anything on any car. There are a few grades in Stainless, but 99% of what you'll come across has very low tensile strength, less that Grade 2, it will cause rusting in short time of any adjacent steel and if fitted stainless fasteners with stainless nuts, will gall. Insulators can be used to reduce or avoid the dissimilar metal corrosion however, unless they are kept clean and well maintained they soon breakdown or are bridged by dirt and become ineffective. Lubricants can be used to reduce the effects of galling (cold welding) reasonably effectively, but are messy and need to be re-applied on every application. They are a total disaster if used with Steel nuts or Steel bolts fitted with stainless nuts. I do not recommend using stainless for just about any application of a car.

 

There's a bit or Factory Info here, though they referred to Setscrews as Screws and they do give a description;-

https://www.theminif...er-information/

 

[alpder]

Your question has, sadly, brought out my inner geek. Be warned that what follows is properly nerdy (awoooga)...

 

Colloquially, in the UK at least, some types of bolts* get called "screws" and some types of screws* get called "bolts". Even by engineers. The term "set screw" invariably means a fully-threaded fastener with a thread that does not taper. The term "bolt" is used more flexibly to mean a fastener with a thread that does not taper and which may or may not have an unthreaded portion.

 

The reason for the mixture of colloquial uses of the words when applied to fasteners is that "bolt" and "screw" are really engineering terms that relate to joints, not to the fasteners used to make those joints. A joint is "bolted" if a threaded fastener (whether or not is has an unthreaded shank) is passed through two or more unthreaded drilled parts, and is clamped onto those parts with a nut. A joint is "screwed" if the fastener threads into one of the parts. Or put another way... if you can shove the fastener clear through the joint then you've got a bolted joint. But if you have to rotate (i.e. screw) the fastener into the joint then you've got a screwed joint.

 

So a set-screw can also be used to make a bolted joint. And a [shanked] bolt can also be used to make a screwed joint.

 

Frustrating, isn't it? If you want to buy fasteners which specifically do, or specifically don't, have an unthreaded shank, the unambiguous terms "fully threaded" and "part threaded" are your best bet. That way, when you come across ebay listings offering "partially-threaded screws" and "fully-threaded bolts", your brain won't explode.

 

*There are, of course, screws that can't be called "bolts": woodscrews for example - they have a tapering thread so they can't be fitted with a nut and therefore must be threaded into one of the parts of the joint itself. And woodscrews - imperial ones at least - generally do have a shank except in smaller sizes. There are also bolts that can't be called "screws": coach-bolts, for example, which have a head that prevents them being rotated into the joint. And, yes, you can buy "fully-threaded coach-bolts".

 

Nerd-alert ends.

Edited by alpder, 12 November 2024 - 02:35 PM.

[Ethel]

Higher grade fasteners tend to be black passivated because plating tends to degrade the mechanical properties - "hydrogen embrittlement".

 

Even BL weren't penny pinching to the point of using substandard fasteners. Whatever was holding your Mini together when it left the factory is likely to be the most suitable specification.

[mbolt998]

Your question has, sadly, brought out my inner geek. Be warned that what follows is properly nerdy (awoooga)...

 

 

Thank you for the best explanation of bolt vs. screw I have ever seen. Everyone has strong opinions on this and it's usually easy to point out inconsistencies. But it all makes sense when you relate it to the joint. The same piece of metal can be used as a bolt or a screw. One niggle is what if I weld the nut on? Is that a bolted or a screwed joint? If just a couple of tacks then I would say it's bolted. They're just a convenience to stop it spinning while I tighten it up. But it might be argued that a continuously welded nut is a lazy way to make a tapped part.