Standard Vs. Metric Wrench: Know The Difference with VIDEO

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The benefits of having a fastener tool such as wrench set is immense.

People need wrench to fix their machines. Most people use wrench mainly to adjust nuts and bolts of their home appliances or vehicles, let it be bicycle, car or motorbike.

If you drive a lot, you may often need a wrench set in your toolbox. Moreover, a wrench set is beneficial also for home appliances.

But, wrench comes in various types and shapes. The diversity sometimes become bothering.

For example; if you are living in USA, you may need a standard wrench. Because, most of American appliances operates only with standard wrench.

However, most of modern appliances support metric wrench worldwide. So, if you have just purchased any new machine, you will be needing a metric wrench.

Your trouble would be double after knowing that the size measurements are different in these two unique types of wrench.

If you are a new comer to America, you might be confused with various types of unit that are used here. Because, metric units are being used globally. But. USA use imperial units.

It may boggle your mind to know the difference between standard and metric wrenches.

This article will serve you with detailed descriptions about standard and metric wrench. After reading this, you’d be able to identify them and know how may you convert one with another.

So, without further ado, let’s get started.

Difference Between Standard and Metric Wrench

1. Standard Wrench

The origin of standard wrench can be tracked back to the imperial age. Standard measurement was used initially by the English in Great Britain in 19th century and onwards.

In the 1970s, Society of Automotive Engineers (SAE) started using standard (or imperial) measurement in USA. This measurement system is still popular in America. So, American cars, trucks or machines support standard wrenches.

Imperial measurement system uses units such as inches, feet, miles, yards etc. So, in standard (or imperial) wrench, the measurement is in inches and the fraction of it.

The socket is being measured in inches. The size chart of standard wrench is a little bit confusing. Standard wrench comes in size such as 1/4, 5/16, 11/32, 3/8, 7/16, 1/2, 9/16, 5/8, 11/16, 3/4, 13/16, 7/8, 15/16 and 1.

If you are using a low end wrench set, it might not include all of the sizes being used. So make sure to purchase SAE wrench based on its use. For example, if you need wrench to fix your truck, you need bigger ones.

A 1/2˝ wrench can provide you with plenty of torques in that case. If you just want to fix your bicycle, smaller wrenches will do. The most used wrench is a 3/8˝ wrench.

Most of the wrenches are double ended. It provides the facility of open ended wrench in one end. In the other end, it is a box ended wrench. Both ends usually fit the same size of bolts.

2. Metric Wrench

The measurement system that is universally accepted, recognized and being used in most parts of world is the metric measurement system. Imported cars are using metric measurement for over two decades.

In this measurement system, units are based as outlined by SI (International System of Units). Commonly used units are: meter, kilogram, ampere etc.

In metric wrench, the socket is measured in millimeters and in round figures. It refers to the length of the nut or bolt that can be adjusted with the wrench.

Commonly used size in metric wrench varies from 4 to 18 millimeter.

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How to Know the Difference Between With Them?

To answer the question, first you need to understand the purpose that prompted the question.

We often encounter with bolts which doesn’t fit in our wrench.

So, how can you tell if it’s a metric bolt or imperial bolt?

Well, metric bolts usually have a number identifier on itself. The number shows the strength of the bolt. Higher number indicates stronger bolt. Imperial bolts typically use markings on it.

Another notable difference is, metric fasteners are coarser than their imperial counterparts. Let’s expound more about their differences. 

Identifying Features

Standard and metric wrench are actually harder to tell apart especially when they both have the same packaging. In order to tell the difference between, you will have to take a closer look at it. If you’re just standing from afar, it will be hard to tell apart. 

The main identifying feature difference they have is their measurements. Standard wrenches have their measurements on edge. Also, if you look closely, standard wrenches use the number of infractions while the metric uses whole numbers. 

Method of Measurements

We already established that both wrenches use different measurements. They also differ when measuring width, diameter, and length. Metric wrench uses centimeters, millimeters, meters, and so on. They usually use a decimal point in between. 

Whereas, standard wrenches use inches and feet. Therefore, you will mostly encounter measuring with fractions. Hence, it is important that you choose the right type of wrench. Using the wrong type may affect the nuts and bolts with their function. 

Always use the correct type for your bolts to prevent any damages. Make sure to check first before using. 


It’s also easier to tell both apart when you find them in the shop. That’s because of their pricing. Generally, metric wrenches are more expensive. It’s not only because it’s the most used wrench outside of the U.S.

Metric wrenches usually come with a lot of pieces within a set. Hence, they’re usually sold in huge sets for different applications. Standard wrenches can be bought as single pieces. 

While being expensive, metric wrench sets bring a lot of versatility so you will have the tools you need for most nuts and bolts. 

Global Application

When it comes to application, standard wrenches are generally catered for North American use. Most of North America uses the American system. Therefore, most of them use the standard wrenches that use the American system of measurement (inches and feet). 

Metric wrenches are commonly used worldwide outside of the North American region. They are made for nuts and bolts that use metric measurements. Measurements you usually know as centimeters and millimeters. 

To sum it up, the type of wrench you gonna use depends on what type of nuts and bolts you’re dealing with. If they use metric measurements, then you have to use a metric wrench. The same goes with a standard wrench with the American system of measurement or imperial measurement. 

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How to Substitute one with another?

Metric or imperial bolt do not perfectly fit with one another. If the bolt is older, using metric wrench in imperial bolt may end up making the situation worse.

On the other hand, if you know how to substitute one for other, it may be helpful.

Suppose, your friend’s car need a quick fix on the road. You have a set of metric wrench with you. But, the car has imperial bolts.

If you know how to convert your metric wrench in conventional imperial units, you might be able to help.

We have already mentioned that, imperial measurement system uses inches and the fraction of it.

So if you can just convert millimeters in inches, you have a fighting chance.

We know, 1 millimeter is equal to 0.03937 inches.

So, a 1/2˝ imperial wrench actually refers to 0.5 inches.

It can be substituted with a 12 or 13 mm metric wrench.

For, 120.0397=0.472 inches and 130.0397=0.512 inches.

Imperial to Metric Conversion Chart

If you frequently need to use metric wrench in machines that use SAE measurements, the following chart may be helpful.

Standard Wrench

Original Size in

inches fraction.

Inches Decimal
5/32˝ 0.156
7/32˝ 0.219
5/16˝ 0.313
13/32˝ 0.406
15/32˝ 0.469
9/16˝ 0.563
5/8˝ 0.625
11/16˝ 0.688
Metric Wrenches that are close

Size in Millimeters Inches Decimal
4 0.157
6 0.236
8 0.315
10 0.394
12 0.472
14 0.551
16 0.630
18 0.709

From this chart, you can notice that all of the wrenches do not perfectly fit. However, a 5/32˝ standard wrench is almost as same as a 4 mm wrench.

You may print this chart, if you regularly need to work with imperial bolts by metric wrench.

We usually recommend to have both sets of wrench.

That’s all about standard wrench and metric wrench.

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