Standard Vs. Metric Wrench: Know The Difference with VIDEO

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

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 cheap 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.

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.

How to Know the Difference?

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.

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

















Metric Wrenches that are close

Size in Millimeters

Inches Decimal

















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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