Key Difference Between Bolts and Screws - Easy to Tell

Bolts, screws, nuts and washers are the most common types of fasteners. Some of them are easy to tell, but there’s always a lot of confusion when it comes to bolts and screws. Although bolts and screws look alike, they are two unique fasteners. There are many differences between bolts and screws in factors like structure, application, cost, etc.

Take five minutes to read this post, you will have a clear understanding of what bolts and screws are and how to easily tell them so that you can apply them correctly and effectively. 

1. What are bolts?

A bolt is a kind of fastener that consists of a head and a screw rod with external threads. Under normal conditions, the threads on the rod are relatively aclinic and the screw tooth pitch is usually short.

The head of bolts will have different shapes, such as hex, flange, T type, square, round and so on. Many bolts are named after different head shapes like Hex Bolts, T Bolts, Flange Bolts, etc. The tail of the bolt is generally flat, and the diameter is larger than screws’, thus the whole part is generally thicker and larger.

A bolt should be used in conjunction with a nut, and it can be inserted through the holes in assembled parts by torquing the nut. Bolts are also usually used with washers, which help to spread the load over a larger surface area, reducing wear and increasing the service life. So compared to screws, bolts provide larger holding strength. Besides, this kind of connection is a detachable connection because the nuts and washers can be easily removed. So bolts are easy to maintain or replace. 

There are many types of bolts commonly used, such as Hex Bolts, Carriage Bolts,  Heavy Bolts, Anchor Bolts, U-bolts, T-bolts, Shoulder Bolts, etc.

2. What are screws?

A screw also consists of a head and a screw rod with external threads, while you can find a clear distinction between a screw and a bolt. Let’s see the image below. You will notice that the thread of a screw is generally oblique,  showing a certain thread angle, and the pitch is much longer than that of a bolt. Besides, the tail is usually pointed, to facilitate the screw into the media. As a whole, a screw has a smaller diameter, thus the whole part is slender and smaller.

The head of the screw will have a drive of Slotted, Philip, Hexagon or other shapes, and the head can be torqued by using a screwdriver of the corresponding shape. In this way, the screw can match with the pre-formed internal thread or form its own thread. 

Screws are often used when bolts are not available. For example, when one of the linked objects can not be punched, then you will have to machine threaded holes on it and apply a screw. Typical screws are Machine Screws, Self-drilling Screws, Self-tapping Screws, Drywall Screws, Chipboard Screws and Wood Screws.

3. Confusing special bolts and screws

Most bolts and screws can be easily identified by the difference in the shape described above. However, it is not inclusive. Sometimes there is no obvious distinction between them, some bolts and screws are still difficult to distinguish.

Machine Screw

This is a kind of screw that looks like a bolt. The end of the screw is flat as the bolt. This kind of screw is generally short with a round countersunk head or hexagon head. It is often used together with a washer to fix metal parts and panels together.

Hex Bolt vs Hex Cap Screw

Hex Bolts are bolts with a hex head, they may be partially threaded or fully threaded. Hex cap screws also have a hex head, the key difference is they may have a built-in shoulder (flat washer facing) under the head, which increases the tensile strength.

4. Difference between bolts and screws

Structure

Screw: Pointed tail, oblique threads, longer pitch, thinner and smaller body in general.

Bolt: Flat tail, aclinic threads, shorter pitch, thicker and larger body in general.

Tools

Screw: For screws that have a groove/drive, use a screwdriver to torque the head of the screw. For special screws like Lag Screw, apply a torque wrench.

Bolt: Use a torque wrench to torque the nut.

Application

Screw: Light to medium construction projects like framing

Bolt: Heavy-duty projects that need regular maintenance and to be easily disassembled. Bolts’ usage has a low requirement for accuracy.

Medium of parts

Screws: Pressboard, Sheet metal, Deck planks, Drywall

Bolts: Studs, Concrete, Beams

Cost

Thousands of fasteners may be used in a big heavy project. For such projects, the cost of using bolts and screws can be a big factor. Applying bolts may often be more expensive than screws. In spite of this, it will save you money in the long run by choosing the right fastener.

After reading this article, I believe now you have mastered the key difference between bolts and screws and can easily tell a bolt from a screw. It is always the first step before you buy and use them. If you have any other questions, welcome to contact us, our email address is info@cngoshen.com. Goshen Hardware is always ready to offer the best fasteners!