The Difference Between Bolts and Screws

Many of us tend to use words interchangeably each and every day.  Most of the time that is not a problem, but on occasion each of us slips up and misuses a word in place of another and just gets it wrong.

Determining whether to utilize the word, “screw” or “bolt” is a quandary plaguing our world on a daily basis.

So here at Ritter we decided to tackle the question of their differences so that you can hold your own during your next home improvement discussion with your friends.

Difference Between Screws and Bolts

Sadly, a universally accepted distinction between a screw and a bolt does not exist. The Machinery’s Handbook describes the distinction as follows:

“A bolt is an externally threaded fastener designed for insertion through holes in assembled parts, and is normally intended to be tightened or released by torqueing a nut. A screw is an externally threaded fastener capable of being inserted into holes in assembled parts, of mating with a preformed internal thread or forming its own thread, and of being tightened or released by torqueing the head. An externally threaded fastener which is prevented from being turned during assembly and which can be tightened or released only by torqueing a nut is a bolt. (Example: round head bolts, track bolts, plow bolts.) An externally threaded fastener that has thread form which prohibits assembly with a nut having a straight thread of multiple pitch length is a screw. (Example: wood screws, tapping screws.)

Now we are sure your eyes have glazed over, and if anything you are even more confused than when you started reading this.

Let’s try and make this a bit easier to understand

In simple terms, a bolt requires a nut in order to be tightened while a screw does not.

Easy, right?  Well, not quite.

You see there are some exceptions to these rules that tend to cause nothing but confusion.  For example, hex cap screws versus hex bolts, or lag screws versus lag bolts. Both of these completely ignore the definition written in The Machinery’s Handbook.  The fact of the matter is that in these cases the names are used interchangeably and it is totally acceptable.

Confused again?Confused about Bolts and Screws

A lot of the confusion comes from the original usage of the terms screw and bolt.

From the beginning a screw was understood to be a threaded item used as a fastener.  A bolt, on the other hand, was not threaded. It was merely a metal rod that passed through materials and was secured on the opposite end by methods such as clinching or pinning. Over time this simple method of separating the two became blurred by technological advances.

Another distinction often made between the two is that screws are smaller than bolts and tend to be tapered.  However, even that difference is contradicted time and time again.

When all’s said and done, the most widely accepted differentiating features of bolts and screws are these:

ScrewsScrews –are threaded in such a way that they fasten themselves within the material and do not require a nut to be tightened.

Bolts – are threaded to allow a nut to be fastened to the end opposite the head.  To do this a bolt must pass through the items it is fastening together.

Let’s take a look at some basic varieties of screws and bolts.

Wood Screws

As the name states, these are meant to be used in wood.  They come in a variety of head styles and are normally threaded for approximately two-thirds of their length.

Drywall ScrewsSheet Rock Screws

Drywall screws are generally threaded the entire length of the screw.  Most often the head has a Phillips slot.  Their primary use is to secure wallboard.

Machine Screws

Machine screws are used to put metal parts together.  They come in a variety of head types and lengths. Machine screws are one of the “exceptions” to our rules in that while they normally thread themselves directly into a hole within the metal, they do, on occasion may be used with a nut.

Sheet Metal Screw

Sheet metal screws are self-tapping and are used for fastening metal components such as flashing.

Lag Screws

Lag screws and the name lag bolt are used interchangeably.  The threads are course and run up about half of the screw…bolt (your call).  The heads on these “screws” are hexagonal or square and they are often used in deck construction.  Unlike the other screws we’ve discussed, lag bolts/screws are driven with a wrench or socket.

Stove Bolts

Stove bolts are threaded from the top to the bottom and always require the use of a nut to fasten it.  The stove bolt believes in obeying the rules we’ve outlined.

Carriage BoltCarriage Bolts

Carriage bolts are distinguished by their rounded heads and square shaped shaft immediately underneath the head.  The reason for the squared shaft at the top is to prevent the bolt from turning as the nut is fastened and tightened at the other end.

​Well there you have it.  The nuts and bolts of nuts and bolts.  While this may not have clarified their differences totally, it should give you a better understanding as you decide on the hardware you will require for your next home improvement project.  Of course, just to be safe and for your own peace of mind, stop by your local Ritter Lumber location and discuss your needs with one of our trained associates.  We are always ready and happy to help.


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