Screw or bolt?

[gaufridus]

The thread404-132824 re. tapping screws set me thinking about screws and bolts. When is something a screw and when is it a bolt?

Machinery's Handbook (20th ed) defines a screw (amongst other edfinitions) as

'an externally threaded fastener......mating with an internal thread.... being tightened or released by torquing the head'
whilst a bolt is

'an externally threaded fastener.....tightened or released by torquing a nut'

Does this mean that the externally threaded fastener lying in the stores enjoys dual status until someone picks it up and fits it to either a tapped hole (making it a screw) or to a nut (making it a bolt. Or does it mean that until someone picks it up to use it, it is neither a screw nor a bolt?

 

[UcfSE]

While I have no idea what the accepted definition for "screw" and "bolt" is, if there is one, I've noticed that the screws I've seen usually have a point while bolts do not. Maybe that has something to do with it.

 

[vzeos]

I also have no idea what the accepted definition is. It may be that it’s just semantics. But if I had to make up a rule, I would say: If the tool used to torque an externally threaded fastener is a screwdriver then the fastener is a screw. If the tool is a wrench, then the fastener may be called a bolt. The Allen screw, which uses an Allen wrench, is the exception that proves the rule.

 

[rmw]

Been discussed ad-infinitum on this site. Do a search.

rmw

 

[quark]

Technically, I second RGasEng.

 

[gaufridus]

rmw - Oops, should have done a search.

Let's end it now. Enough has been said.

 

[codeeng]

Bolts and screws are differentiated by their thread length. A bolts thread length is a portion of the total length while a screw is threaded all the way. Short bolts would also be considered screws.

 

[wes616]

bolts thread length is a portion of the total length while a screw is threaded all the way.

This unfortunately is not the case either. Screws come in both full threaded and partial threaded shanks. Example being the NAS623 Pan head screw.

Wes C.

 

[IRstuff]

see thread1010-92939

TTFN

 

[codeeng]

Certainly, Machinery's Handbook gives the definition noted by me above, although this may have been taken out of a British Standard. In my days on the drawing board we always specified Hex Bolts and Hex Setscrews. I guess, in the end, it all depends where you hail from.

 

[BillPSU]

What about socket head cap screws.

This is a discussion about semantics and it varies by historical usage.

 

[vzeos]

codeeng: If you’re saying that the first post in thread1010-92939 (21 Apr 04 12:35 ) indicates that the Machinery's Handbook gives the definition noted by you above, you should re-read that post. Or perhaps, cite the post you're talking about.

 

[codeeng]

MH definition:

Length of Thread on Bolts:
"distance from the end of bolt to end of thread, varies depending on nominal length of bolt. Short bolts are threaded as screws."

Length of Thread on Screws:
"threaded to permit a ring gauge to be screwed up to the head within a distance not exceeding 2.5 x pitch (3.5 x pitch for > 25mm diameter)."

 

[codeeng]

I should have added that this definition only holds true for hex bolts and hex screws. I agree that there is confusion on other forms. Perhaps "screw " and "setscrew" would differentiate the thread length here.