How To Measure Socket Drive Size

A socket set is a convenient set of toolkit accessories that lets users tackle various sizes and types of fasteners, primarily geared at fitting a variety of nuts and bolts. Socket sets are typically sold as a single, convenient case, box, or pouch containing various replaceable attachments.

In fact, because there are so many assorted sizes and shapes of nuts, bolts, and other fasteners, no one socket set or socket wrench set will have socket sizes based on every single kind of fastener you’ll encounter.

Sockets for most fastener types are included in most comprehensive sets, although not for all available sizes.

socket drive

Knowing which nuts and bolts you’ll face in your day-to-day job is an important consideration in determining which socket set or size of the socket is best for you at that moment.

In our guide, you can start understanding socket sizes, learn how to measure socket size, and more. By the end, you’ll see how to measure a nut for a socket to avoid it rounding and why you could need metric vs imperial sockets occasionally.


How Are Socket Drives Measured?

When you want to know how to determine socket size, it helps you understand knowing how are sockets measured.

Socket head sizes are calculated using two systems: metric (millimeters) or imperial (inches).

Regardless of whether the drive socket is imperial or metric, the size is always specified in imperial measures.

Sockets are sold in sets that comprise a variety of sizes.

Imperial Sizes

Since 1965, the term imperial will refer to the United States weights and measures system. Around the same time, the UK was adopting the metric system.

Imperial sockets sizes are taken in inches and fractions of an inch, and the socket head size ranges from 5/32′′ to 1 1/2′′ or larger.

Imperial vs metric sockets are used mainly in the United States, yet with Asian manufacturers increasingly supplying parts, there is more demand for metric.


The Society of Automotive Engineers is a standards organization based in the USA. SAE is a non-profit organization focusing on transportation-related businesses, such as automotive and aerospace.

As sockets built for use in the American automotive sector need to follow SAE specifications, SAE links closely to imperial size sockets.

Metric System

Millimeters are used for the metric measurements of a socket set. You’ll often find the typical metric socket head size ranges from 3mm to 80mm.

The metric system is now the most frequently used measurement system globally so that you can find common metric bolt sizes in every country and this metric socket sizes to match.

Since more products are arriving in the USA from other countries, there is no reason to think of imperial or metric socket, as you can need both.

What is AF?

Sockets and socket sets are measured using the American fractional scale. When you have European manufacturers using metric and the US using imperial sockets, AF can confuse as it has two different meanings. (Read How to Screw Into Concrete)

AF is an abbreviation of American Fractional, which is also a synonym for imperial. Although, when used with metric sockets, AF means “Across Flats.” For example, an 8mm AF socket fits a bolt head with flats that are 8mm wide.

To be more confusing, some socket manufacturers use AF to mean their high-quality anti-slip sockets that apply force to your bolt head flats and not on the corners.

What is the Drive Size of a Socket?

14-inch, 3/8-inch, and 12-inch drive sizes are on offer for a metric socket set, Imperial sizes and other unique variations you could come across.

With the main to, each needs a unique ratchet and additional attachments like an extension. Different socket sizes use larger drive sizes, while smaller sockets use smaller drive sizes. Besides this, you find common ratchet sizes and an adapter that enables you to use one ratchet on smaller socket tools to meet your needs.

Common socket sizes are available in a variety of socket sets that are metric and imperial. You can even find they come as a combination socket set and accommodate a wide range of socket types from the one ratchet handle.

The drive socket’s dimensions have four common socket sizes and will always be measured in imperial units as it is an international standard. The drive socket size most common are 1/4″, 3/8″, 1/2″, 3/4″, or 1″.

Small hand tools socket sets will be 1/4″ or 3/8″ drive sockets as they are better suited to work in tight spaces.

Large socket sets can be 3/4″ or 1″ drive sockets as these tools are needed for larger fasteners. A greater socket size means a larger drive socket, and which can deliver high force and torque without putting the tool in harm’s way.

What is a 1/2 Inch Drive Socket?

The half-inch size of the drive represents the middle ground between what we know as a small socket or a large socket. The 1/2″ drive socket standard sits in the middle of the standard drive socket sizing range.

You find this an essential component from leading brands in many of their chrome-molybdenum steel sockets to deliver strength.

As you move up in the size of the driver hole, you’ll have more six-point sockets as the torque size increases, such as those in impact sockets.

How Are Sockets Sizes?

The range of fastener sizes that socket sets are meant to fit over is usually the most significant distinction between them, and we’ll go through some of the most popular sizes and kit configurations in the following sections.

If you want to know how to make socket sizes readable, one pro-tip is to fill the groves with correction fluid.

It’s also important to understand the many sorts of sockets that can be purchased as a package. The following are some of the more popular socket wrench kits:

Impact Sockets

Impact driver socket sets work similarly to conventional socket sets, except that they’re made for use with power tools like electric or pneumatic air wrenches. You can use them on a conventional socket wrench as the square hole in the socket is the same.

Impact sockets are forged from slightly softer but thicker alloys like chrome-molybdenum steel and are typically dipped or coated to provide better anti-corrosion qualities to sustain use in these high-demand applications.

Imperial Sockets

Socket sets in imperial are for fasteners with heads measured in inches and fractions of an inch. While the socket head opening is offered in metric measurements, the drive socket recess where the component connects the socket and ratchet spanner will always be in imperial measurements.

Likewise, you always find the overall socket length for spark plug sockets longer than the socket length of a regular deep socket. Spark plugs have the upper part that interferes with regular types of sockets.

Metric Sockets

Metric is measured in millimeters and regarded as more precise by leading brands. With metric, you find there are no in-between sizes as they run in single increments.

Another thing to note is when the size of the drive for imperial doesn’t have a socket, a metric socket can often be used as an alternative on your inch socket and driver tool. You will find you can use your handle from a metric kit as it uses the same drive hole as imperial, and your wrench size will fit your different socket wrench sizes.

Deep Sockets

You’ll find these in smaller kits or sold separately as compared to normal sockets. Unless you are working professionally in the auto industry, you’ll find standard-length sockets, plus a smaller selection of deep sockets. Deep sockets are not used in confined spaces, so they may not be of use for most occasions.

hex socket

Hex Sockets

Hex socket sets or 6-point sockets fit over a hexagonal nut or bolt head. Such a socket is popular for everyday use as they’re adaptable and can fit a wide range of fasteners. The wrench size and drive hole are the same as in other kits: the square drive hole and the same wrench size lug that fits inside it. (Read Allen Key Sizes Chart)

A 12-point socket set also accommodates a square drive hole and common wrench size.

Ratchet and socket sets are typically used to tighten or loosen a variety of fastener sizes and types. Many basic socket sets have attachment sizes to meet the most common sizes of nut and bolt gauges on cars and other vehicles.

Six-point socket sets, besides being convenient, can make certain activities easier by adding a layer of user-friendliness.

If you are dealing with particularly difficult or rusty fasteners, a well-stocked six-point socket set lets you select a socket that fits perfectly over the nut or bolt head. (Read Star Bits Sizes Chart)

Most sockets encircle a nut or bolt head, yet 6-point sockets are preferred to a 12 point socket as you get a better grip.

How To Measure Socket Drive Size (1)

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