The Difference Between a Bolt and a Screw

[sssfox]

I learned something today.  I was looking through the Machinery's Handbook, trying to find the dimensions of really small fasteners.  The smallest I could find was 1/4" by the way.  I found a section on bolts and screws.  I can't say I've really thought about it, but thinking back, I figured a screw had a slotted or Phillips head and a bolt had a hex head, but that's not the case.

According the the manual, basically, if it is used with a nut, it is considered a bolt and if it is intended to be used in a tapped hole, it is a screw.  AND, if it doesn't fit the primary criteria of a bolt, it is probably a screw.

So it has nothing to do with the design, only the intended use.  I had no idea. 

The information is on page 1426 of the large print edition of the 28th edition.

Steve Fox

[b.lindsey]

Interesting Steve. I am surprised that 1/4" was the smallest you could find though. It may be that the smaller sizes are in another section of the handbook (i.e. number sizes rather than fractional sizes. I am sure they are there somewhere. Both of my copies are at work at the moment but I will look on Monday.

Bill

[sssfox]

Thanks.
I've been having much more trouble finding the specs than I thought I would.
Seems like hardly any table I can find that lists the head and nut sizes goes below 4-40.
I can find plenty that have the thread sizes, but I don't need those.

Steve Fox

[sssfox]

After your comment, i looked a little further.  I found a table that goes down to 1 about 160 pages further along.  I guess I'll have to live with that. 

It says a #1 head is between .120 and .125 across the flats.  Does that sound about right?

[b.lindsey]

That sounds about right. If you need across the flats dim for a 0-80, let me know. I can measure one for you tomorrow. You might try googling nut dimensions too. There are some interesting tables of info out there.

Bill

[crueby]

The folks at American Model Engineering Supply have a table at this page that gives dimensions for the scale bolts that they supply, which are quite good looking on a model, patterned after full size ones. I've (and I know many others here have too) bought some excellent stock from them.

http://www.americanmodeleng.com/id41.html

[Jasonb]

The way I was always told is that a screw is threaded all the way upto the head and a bolt has a section of unthreaded shank with just the end threaded. Whether its used with a nut or not makes no difference. This applies to hex head screws/bolts and not screws driven by a screwdriver.

One thing to watch when looking at the likes of Machiney's is that for these models of old engines you don't want to be using tables for modern fixings, the older ones were smaller hex, taller and mostly single chamfer. Crueby's link which I also posted in your other thread has the smaller spec hexes.

Take a look at this post and my one after it to see how modern nuts and old style nuts differ

http://www.modelenginemaker.com/index.php/topic,5606.msg109029.html#msg109029

[Stuart]

That's the way I was brung up , and that was the way we ordered them from the stores , you got the nut with bolt orders but order setscrews you ordered the nut separate ( half or full ). But to muddy the waters there were machined bolts same as bolts but machined all over instead of forged.

We may be into another common language separated by a ocean  same word different object


Studs round bar with a thread at each end wit a plain section in the middle, one end normally threaded shorter this end is screwed into the casting

Stuart

[jadge]

The way I was always told is that a screw is threaded all the way upto the head and a bolt has a section of unthreaded shank with just the end threaded. Whether its used with a nut or not makes no difference. This applies to hex head screws/bolts and not screws driven by a screwdriver.

That is my understanding too.

One thing to watch when looking at the likes of Machiney's is that for these models of old engines you don't want to be using tables for modern fixings, the older ones were smaller hex, taller and mostly single chamfer.

For Whitworth at least the old style hex heads were taller, but the old style hex dimensions were larger, roughly by one size.  So what is now the standard AF for 5/16" BSW used to be specified for 1/4" BSW.

Andrew

[Manorfarmdenton]

In agriculture we refer to an item that is threaded all the way to the head as a set screw, and if only partially threaded as a bolt.  No distinction as to use.

[Gas_mantle]

Although not really true in the strictest sense I tend to still think of a screw as being a tapered fixing for use in wood, plastic etc and a bolt as being a parallel thread for use with a nut or threaded hole.

Peter.

[Stuart]

Worabout a self taper then , hang on they are abidexterouse they wok in metal and that brown stuff called trees

 

Stuart

[Allen Smithee]

A person who bolts can unbolt back to their starting point. But once someone is screwed they can't be unscrewed - that's the difference between people and lightbulbs...

PDR

[Stuart]

Come on Pete you know very well they are lamps

By ek my mentor would have boxed my tabs lamps go in lamp holders and bulbs go in the garden 


Stuart

[Dan Rowe]

I hate the definition on this link but read on to be fully confused by the difference between screws and bolts. Bolts can be fully threaded or partially threaded in the classification standards I have read.

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

Dan