Screws vs Bolts

Ok, this is just something to think about. :smile:

What is the difference between a screw and a bolt?

According to the Structural Analysis Reference Library, this is the definition:

"The correct definition of bolt and screw is as follows. 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 full discussion of misdefinitions and corresponding confusion regarding these two words, see details"


Do you agree?

That’s very confusing definitions. Beginning of the technical school, they were teaching us that, bolts are bigger and half way threaded. Another teacher comes and tells, if it is phillips-alien-straight drive etc. named screw, wrench headed ones are Bolt. This changed back and forward all the way to graduation. I decided to call them two different classes, small screw and big Bolt. If you ask me wich one make sense, really definition is bigger wrench headed screws are actually Bolt. M2c.

They state here that the difference has nothing to do with size, nuts, heads or fully or partially threaded. Just standardization of the threads is important.

I deal with this every day. Isn’t life confusing enough?

Machine Screw = Bolt

Wood Screw = Screw

Self Tapping Screw = Tech Screw, etc.

My $0.02…


Lag Bolt = Screw


I learned in a few engineering classes that the difference is a bolt is fastened using a nut and a screw is not.

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To try and sound cleverer than I am, “a rose by any other name would still smell as sweet” or something like that anyway.

Like fish, plants and people, different communities, countries and trades, all have different names for the same or similar items. Some folk drink “soda”, some drink “pop”, while here in Aus, we drink “soft drinks”.

Ditto for engineering terminology.
Screws have threads. Bolts have threads. Machine screws have threads. Set screws have threads. Threads are also found on leadscrews, clamps, jacks, and a multitude of other things. Some have nuts, some screw into threaded holes, some cut their own threads on insertion.

What you chose to call an item, doesn’t really matter. However if you build an engine with woodscrews, a bridge with soft steel carriage bolts or an XCarve with aerospace spec titanium, your probably going to have quality & cost issues.

If you’re making a thing and you’re not sure what fasteners you need, get some advice from someone who knows what they’re talking about.
Building a kennel - talk to a carpenter.
Building a fighter jet - talk to an engineer.

If you’re looking for long-winded homilies - I’m your man.

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As simple as it is, I think this is the best describe.

Now that is a sensible definition… thanks BetaPrints

Ok, now I am really screwed up…

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Hehehe, me 2 :smile:

@BetaPrints that’s all fine where you may live…

When I did my trade, a “machine screw” or a “cap head screw” was a hex head female bolt (a bolt tightened with an Allen key or hex key) that screwed into a blind hole instead of a nut.

Trade terminology serves two distinct purposes;
It help keep the riff-raff out (middle-aged blokes who think they’re cnc machinists)
It allows endless entertainment when sending apprentices off to pick up bits & pieces from the storeman.

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As a proffesional driver it has always been fun to send the noobs to the shop for blinker fluid and muffler belts. One place i worked actually had a real looking label affixed to a gallon of washer fluid to give to the noob. Then it was even more entertaining to watch them try to figure out where to put it into the vehicle.

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