What is the Difference Between Bolt and Screw?

People generally expect that bolts and screws refer to the same hardware fasteners. But while bolts have similar look and features, they are two different fasteners having their own unique applications. So what is the definition of bolt vs screw?

Bolts Vs Screws: What’s the Difference?

The difference, according to a thesaurus shows there is no difference, as bolts and screws are the same. While it would have been very tempting to lump all of these fixings together (and would have made our job easier!), there are some important differences that a user must take note of before consuming them.

It is true that for the layperson, there does not seem to be much difference between a bolt and a screw. They are both fasteners, they are both threaded, and both have a head for tightening the fastener but there is more to it.

The most obvious difference there is, is that a bolt is not normally threaded throughout its length, as it has a plain section. A screw however, is threaded its full length to the head.

What are Bolts?

Bolts are that non-tapered fastener that utilizes a washer and nut to fasten objects together. Screws are a tapered fastener which will mate with a pre-existing thread or put its own thread in the material as it turns.

Bolts are made to attach unthreaded objects, typically with the use of a nut. Screws on the other hand are used to attach threaded objects. The previously mentioned items as well as screws that attach threaded and unthreaded are not always threaded.

Not all objects create their own thread, while some objects include a pre-thread. The differences is that screw attached threaded objects, while bolts attached unthreaded objects.

Again, screws can create a thread as the screw is being inserted. So, a screw will be turned to attach a joint, while bolts can be tightened down into place with the use of a carriage bolt or tool.

Typically bolts are used to create a bolted joint using a nut to apply force while the shank acts as a dowel. In turn, the joint has the ability to support the joint against sideways forces.

This is one of the reasons that most bolts have a shank that is unthreaded (some manufacturers refer to it as the grip length); in effect making bolts efficient dowels.

There are tens of what seems like an infinite variety of bolts, but for clarity we can refer to bolts as anchor bolts, arbor bolts, elevator bolts, hanger bolts, hex bolts, J bolts, lag bolts, rock bolts, shoulder bolts, and U bolts.

Also, bolts can come in an array of materials, including steel, stainless steel, bronze, brass, and nylon. However, it is said that as much as 90% of all bolts are made of steel, hence making manufacturing companies use steel prefeered over other materials.

What Is A Screw?

A screw refers to a broad category of mechanical fasteners with a threaded shank that allows the screw to be screwed into a part.

Screws come in different shapes like wood screws and self-tapping screws that permit the screw to screw in and cut threads in the mating part, and then there are machine screws that are screw fasteners that are very similar to bolts, but are typically fasteners that have an entire threaded shank, as opposed to bolts that only have part of a threaded length on their shank.

Sometimes bolts and screws are distinguished by their use, and generally speaking in regards of this distinction, a bolt would mate with the parts by passing unthreaded through holes in both parts, and a nut would attach to the bolt and hold the parts together, while a screw would mate with a threaded hole in one part and attach the parts with only the threaded hole.

In most cases we might not use the distinction strictly. The use of the word screw is generally used as the fastener which is not a self-tapping fastener and has only a partial length of threaded shank.

We also generally use the term screw for a fastener that is a self-tapping fastener, or a fastener with a fully threaded shank.

Typically a screw is installed into a threaded hole, unless it is a self-tapping screw creating that thread all by itself. Bolts do not typically require nuts, and are secured by simply tightening into the hole with a driver having a screwdriver or screwdriver bit shaped to appropriate mate with the drive recess.

In most cases to counter any other possibilities, screws are typically shorter than the width of the material that they are secured to in turn there is no protruding of the screw from the other side of the material.

There is not only a large selection of kit screws themselves like chipboard screws, particleboard screws, deck screws, drive screws, hammer drive screws, drywall screws, eye screws, dowel screws, wood screws, twin fast screws, security head screws, sheet metal screws, etc.

There is also a large selection of head shapes for screws in addition to the types, and they all seem to have their own unique head shape(s) for example there are pan, button, round, mushroom, oval, bulb, cheese, larynx, and flange head shapes. Screws are also made in a variety of materials like bolts.

How To Decide When to Use Bolts Instead of Screws

Before choosing a side in the bolts vs. screws debate for your next project, think about these three factors:

Application

The main consideration for your project is whether to use screws or bolts. Remember bolts have superior holding strength, and screws are in between on holding strength.

Screws are more suited for light to medium duty construction projects such as fences or framing. Bolts are used for heavy duty projects. Bolts are best used on a project when the end use of the completed project is greater ease of assembly/disassembly.

Material

Whether you’re using sheet metal, wood, concrete, or drywall for your DIY undertaking, you want to think about how it applies to bolts vs. screws. Material matters.

Materials That Typically Require Screws:

• Plywood
• Pressboard
• Drywall
• Sheet metal
• Deck planks

Materials That Are Usually Best for Bolts:

• Concrete
• Studs
• Beams

Certain materials may pose a choice between a screw and a bolt assembly. For instance, a 2″ x 4″ framed as a stud in a wall section is best with screws while for an application like deck assembly bolts are likely the better option.

Keep in mind the loads being put on the fastener and the material when deciding between bolts and screws.

Cost

Price is a consideration whenever you are budgeting for a project (particularly when you need a large number of fasteners). While bolts may have a higher cost, using the correct fastener will provide considerable savings in the long run.

If unexpectedly you need to repair your project because you used the wrong fastener for the material or application, you are not saving money by going the cheaper route.

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