Bolts vs Screws 6

[ringman]

ASME Y14.5 'tends' to differentiate between bolts and nuts in the Fixed and Floating fastener formula section.

Is there a consensus amongst engineers/designers/cad operators as to the technical correctness of the definition of bolts verses screws?

 

[CoryPad]

This terminology debate has been around for a while. There is no technically compelling reason to differentiate externally threaded fasteners into the two groups of bolt and screw. French and German languages use a single word (vis and schraube) so why can't English? Since the helical pattern is called a screw thread, I think screw is the natural choice.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[CorBlimeyLimey]

http://euler9.tripod.com/bolt-database/boltdef.html

Bolts are defined as headed fasteners having external threads that meet an exacting, uniform bolt thread specification (such as M, MJ, UN, UNR, and UNJ) such that they can accept a nontapered nut. Screws are defined as headed, externally-threaded fasteners that do not meet the above definition of bolts.

http://everything2.com/index.pl?node_id=1272695

The short rule is, if it has a nut, it's a bolt. If it doesn't, it's a screw. I hope this clears things up, but expect that I won't change common usage.

http://www.bicyclesports.us/id193.htm

 

[MintJulep]

thread1010-92939

 

[GBor]

Your original post comments on Bolts and Nuts which are externally vs. internally threaded fasteners, but your question asks about bolts vs. screws. Technically, the term is "Threaded Fastener"...no differentiation between bolt or screw.

 

[TheTick]

Pins are actually "bolts", bolts are actualy "screws".

 

[ringman]

Looks like their aint no consensus.

 

[ctopher]

Here is more info. My company concurs.

http://www.boltscience.com/pages/faq.htm#14

Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 06/08
ctopher's home (updated Jul 13, 2008)
ctopher's blog

 

[ringman]

ctopher,

Thanks, that helps a lot. Mon I will research the B18 standard for screws.

 

[ctopher]

You're welcome.

Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 06/08
ctopher's home (updated Jul 13, 2008)
ctopher's blog

 

[ajack1]

Wow that seems like a simple question so why cannot I think of a simple answer?

The problem as I see it with the answer from Corblimeylimey and ctopher is that if you use say a M6x20 countersunk screw/bolt to clamp a plate to two other plates one thick and one thin, in one instance you use a thread and in the other a nut and washer so the same fastener becomes both a M6 countersunk screw and a M6 countersunk bolt.

My personal preference is bolts have external drives on them, be that hexagonal or even square (like a coach bolt) whilst screws have internal drives on them, like Phillips or Allen, however I am sure there is a very good reason why that is wrong.

I am sure this thread will have a few more twists and turns in it.

 

[ewh]

The general rule of thumb as I learned it (for what it's worth) is that the difference is which part is being torqued. A screw is torqued through the screw head, a bolt is torqued through a nut.

When the people fear their government, there is tyranny; when the government fears the people, there is liberty. - [small]Thomas Jefferson [/small]

 

[KENAT]

I believe the US customs or whoever it is has a definition as bolts & screws are taxed differently but I can't remember the reference.

CBLs first link

http://euler9.tripod.com/bolt-database/boltdef.html

sounded very definitive but didn't appear to give any kind of reference as to where that definition was obtained from.

Plus based on several of the definitions, where do set screws fit in?

I long ago gave up trying to work out the difference and if I care for an application make sure the threaded fastener I call up has an adequate description, preferably a spec.

KENAT, probably the least qualified checker you'll ever meet...

 

[TheTick]

Fastenal is not completely consistent w/ its terminology. For hex head threaded fasteners it's about 90% "Hex Head Cap Screw" & 10% "Hex Bolt".

Most of the old-school heavy-metal places I worked at in WI use "screw" for anything w/ threads, including hex head.

 

[drawoh]

ringman,

Try working out positional tolerances from first principles.

A bolt, a cotter pin or a non-countersunk rivet can be assumed to be located exactly at nominal position. Your clearance holes must clear an area at least the diameter of the fastener, located exactly at nominal position. As the hole gets larger, it can shift off nominal, hence the MMC specification.

A screw, a dowel pin or a fabricated feature is located by a positional tolerance. The clearance hole located excactly at nominal position, must clear an area equal to the diameter of the fastener plus the positional tolerance. Again, an increased diameter allows positional error.

JHG

 

[btrueblood]

Um, in your original post, ringman, "ASME Y14.5 'tends' to differentiate between bolts and nuts in the Fixed and Floating fastener formula section."

I believe you mean they differentiate between bolts and screws ?

I.e. between floating fasteners (threaded fasteners with nuts) vs. fixed fasteners (fasteners threaded into tapped holes on a single parent body). The tolerances required for position of the fasteners will change depending on those circumstances, as you know having read that section.

Or maybe I am misreading things...it is Monday after all.

 

[CheckerRon]

I am with AJACK1 on this subject. If I can turn it with a wrench, it's a bolt. If I need an allen, torqs or screwdriver, it's a screw.
This was generally how the old MS specs seemed to categorize them.

 

[ctopher]

What about Lag Screws? There are both types, install with a screwdriver or a wrench.

Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 06/08
ctopher's home (updated Jul 13, 2008)
ctopher's blog

 

[drawoh]

ctopher and CheckerRon,

How about cap screws, as opposed to socket head cap screws? Cap screws have hexagonal heads.

There is a contect to this terminology that has nothing to do with how we turn the fastener.

JHG

 

[CheckerRon]

Some people call them lag bolts.
I thought about hex head cap screws, but was kind of ignoring them. I didn't say it was a hard rule, I said that's how I think of them.

It seems from the concensus of this post, that there is a context to the termminolgy, but no one is really sure what it is.

Again, ignoring the anomoly of the Hex Head Cap Screw, I like my Dad's definition best:
"Bolts are big and screws are little."