What is the difference between Bolt and Screw? 1

[allenchu]

Is anyone can provide the EXACT definition of BOLT and SCREW?

 

[wes616]

thread404-133038

Many many threads on this topic in various fora. Use google to search eng-tips.

Wes C.
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No trees were killed in the sending of this message, but a large number of electrons were terribly inconvenienced.

 

[meintsi]

Short answer:

Screws are held by the material and are usually compressed by it.

Bolts typically use nuts or some sort of a compatible threaded interface.

Long Answer:

Bolts are 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 headed, externally-threaded fasteners that do not meet the above definition of bolts.

for more info............

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

Remember...
[navy]"If you don't use your head,[/navy]
[navy]your going to have to use your feet."[/navy]

 

[wes616]

meintsi,

Screws are headed, externally-threaded fasteners that do not meet the above definition of bolts.

. This is not true! Many many screws must meet a thread specification. Let me name a few, NAS601+, NAS514, NAS623, NAS517, NAS8602, MS3212, AN115601, MS16198, ETC ETC.

You answer may be (somewhat) true for wood type screws, but I'm sure it's incorrect for machine type screws.

Basically the answer is there is no one real answer. This debate is as old as mechanics, and I'm sure comes down to two guys (in the beginning) with competing products. 'SREWS ARE BETTER --- NO BOLTS ARE BETTER --- NO SCREWS --- BOLTS,' you get the idea. The both fall under the category of threaded fasteners.


Wes C.
------------------------------
No trees were killed in the sending of this message, but a large number of electrons were terribly inconvenienced.

 

[meintsi]

Wes,
Love the bolt-screw debate above....

... having external threads that meet an exacting, uniform bolt thread specification ...

Yes, screws do have many of their own thread specifications, but even the mil/aircraft examples you give all refer to them as "screw threads" not "bolt threads". Yet many of the screw threads listed above have many form tolerances tighter than bolt threads. When a bolt is tightened, the forces on both sides of the thread are different. This helps to explain why many of the screw thread forms currently used on the space shuttle are asymmetrical.

The terms have become so interchangable that "trustworthy" sources such as the Machinery's Handbook and some Military Specs both incorrectly call bolt-threads, screw threads. Because of this, there will always be fuel for debate.



But by formal definition, if it does not meet the bolt thread specs, it is technically a screw.



Remember...
[navy]"If you don't use your head,[/navy]
[navy]your going to have to use your feet."[/navy]

 

[wes616]

Meintsi,

I do understand what you are saying regarding screw thread specification. However, I have just looked up the thread form specs for two random bolts, an AN Bolt, and a NAS1103 Bolt, and they both refer to Screw Thread Specifications.

Mil-S-8879: SCREW THREADS, CONTROLLED RADIUS ROOT WITH INCREASED MINOR DIAMETER, GENERAL SPECIFICATION FOR (S/S BY SAE-AS8879)

and

Mil-S-7742: SCREW THREADS, STANDARD, OPTIMUM SELECTED SERIES: GENERAL SPECIFICATION FOR

SOO... speaking of soapboxes

Wes C.
------------------------------
No trees were killed in the sending of this message, but a large number of electrons were terribly inconvenienced.

 

[2dooks]

Hi,

Not all of the replies are strictly true. So many people use different nomenclature. Here in the UK a hexagon head bolt (acp screw in the US) would become a Hexagon Head Set Screw, if it were threaded to the head....

Hope that helps!!!

 

[swall]

My own self satisfying definition--If it's 1/4" dia or bigger, it is a bolt. If smaller, it is a screw.

 

[bugnut]

When I was being trained as a machinist this question came up. Here is the explanation and it made sense then as it does today-A screw has no nut, hence a threaded fastener alone is a screw, when a nut is added it becomes a bolt. Further this was explained as a hens egg, when laid or sitting in a carton it is an egg, if it hatches it is chicken, if it never hatches it is an egg.

 

[JohnNabors]

I imagine there are probably exactly as many answers to this question in this world as the total number of human chromosomes divided by 32.

 

[ietech]

Look in Grainger, Fastenal, McMaster Carr or other fastener supplier catalogs and see how they are sold. It is the best way to get what you want. In McMaster Carr there are very helpful explanations of "What Is A ???" for most of the products in the catalog. This is not an engineering answer but a communication and practical one. It is always helpful if your supplier understands what you want, or you understand what is over the counter available.

 

[jbel]

What is the difference between a motor and an engine???

 

[JohnNabors]

How about this one? If you tighten it and it strips, it's a screw. If you tighten it and the head snaps off, it's a bolt.

John Nabors

"Against stupidity the very gods themselves contend in vain." - Friedrich von Schiller