Metric & Standard Bolt & Screw Size Chart: M2, M4, M5, M6, M8, M10 (2023)

Bolts and screws are integral parts of fastening or assembling things. Many people assume that these two materials are the same, but they are different. Physically they look similar. They are still unique fasteners in terms of application.

Screws are very versatile, making them a popular choice among people. The threads ensure a stable hold, so they can meet the needs of any project. They come in different types and sizes that you can use in metal and wood. OtherTypes are used for drywalland concrete.Screws are self tapping, but you still have the option to drill a hole for it. If you choose the latter, it will take less time to drill all the holes before installing the screws.


Metric & Standard Bolts & S...

Metric and standard stud bolt sizes are determined by length and thread count. The easiest way to find these out is to consult our screw size chart below. However, here's a quick overview from the chart:

  • The screw size M2 has a diameter of 1/16 inch.
  • The screw size M4 has a diameter of 7/64 inch.
  • The screw size M5 has a diameter of 1/8 inch.
  • The screw size M6 has a diameter of 9/64 inch.
  • The M8 screw size is 5/32 inch in diameter.
  • The M10 screw size is 3/16 inch in diameter.

Table of contents

  • How to determine the screw size?
  • How do I know the screw size?
  • shopping guide
  • The type

Standard and Metric Bolt Size Chart

Here is the standard and metric screw size chart you need to find the right products in the shop! It doesn't matter whether you work outside or on furniture. ASME is the organization responsible for much of the standardization work. These standards dictate things like thickness and screw threads.

SizeMillimeterCustomsnext breaklarge diameterpitch diametersmall diameter

Screw size M2

We use the M2 screw in small items, such as B. electrical appliances,Cameras, and cell phones. They are also common in laptops and the like. The "M" corresponds to the outer diameter in the metric system, so an M2 has a diameter of 2mm. Keep in mind that in reality the actual diameter would vary between 1.9mm and 2mm due to manufacturing tolerances.

N. Some manufacturers offer non-standard pitches, so it's best to contact them if you have concerns about customization. If themeasurement readsM2 x 8, the diameter is 2mm and the length is 8mm.

brass, nylon, stainless steel,Stahl, aluminum and titanium are some of the materials used in the manufacture of this type.

Screw size M4

An M4 screw is slightly larger than an M2. The M4 is available in multiple lengths but shares the same 4mm diameter. The M4 screw size in inches is equal to 0.15748.

Screw size M5

Metric & Standard Bolt & Screw Size Chart: M2, M4, M5, M6, M8, M10 (1)

The screw size M5 has a diameter of 5 mm. The dimensions of the M5 are significantly thicker than those of an M4, but can be used in multiple applications. Some have an anti-corrosion coating to prevent thisRostfrom construction.

The M5 screw size in inches is 0.19685 inches.

(Video) How to Read a Metric Screw Thread Callout

Screw size M6

The diameter of an M6 screw is 6 mm. It is available in several thread pitches, e.g. B. 12-24 and 10-32. An example application of an M6 is mounting the device on the vertical posts of a rack. We typically use the above threads in rack applications.

Screw size M8

An M8 screw has a diameter of 8 mm. It has a pitch thread of 1.00mm for fine and 1.25mm for standard.


The M10 bolt has the largest diameter among these six types. It has a diameter of 10 mm and is available in several lengths. The M12 is even wider and can carry heavier loads.

How to determine the screw size?

Metric & Standard Bolt & Screw Size Chart: M2, M4, M5, M6, M8, M10 (2)

When examining and determining screw size dimensions, you need to understand two things - length and number of threads. The latter is also commonly referred to as threads per inch (TPI) or thread pitch. We use the TPI to determine the gauge of the thread. The number also indicates whether a screw can be screwed through a bolt. To measure the screw size, we take its diameter. When the measurement says 1/4-20, that means it's 1/4 inch in diameter and 20 threads per inch. A ruler is all you need to determine the number and size of threads.

Metric & Standard Bolt & Screw Size Chart: M2, M4, M5, M6, M8, M10 (3)

The first step in measuring length is to find a surface to lay it down on a flat surface. Start measuring where the head would rest when fully embedded in something. In some cases you may need to hang it from the edge of a surface to lay it flat. Those with a pan, round, or traverse head should be measured from the bottom of the head to the top. Those with a flat or oval head should be measured from tip to tip. Hex heads are an exception to this rule, which means you must measure from the bottom of the head.

Now that you know how to take the measurement, the next step is to place the ruler along the axis to get the thread count. For accuracy, count the first thread as zero. Count the number of thread gaps within one inch of the length. Once you have these values, you can now divide the length by the number of thread gaps. If there are four thread gaps in a one inch length, the thread pitch is 0.250 inch (one inch / 4 thread gaps = 0.250 inch). In other words, the spacing between each thread is .250 inches and it has a threads per inch (TPI) of four.

Put it back on a flat surface. Using a ruler or tape measure, measure from one side of a thread to the other to get the diameter. The diameter in the imperial system is represented either as a fraction of an inch or as a measurement. If you use themetric system, use the cm or mm side of the ruler to measure the diameter. Remember that when purchasing measurements listed in the metric system, the first number is the diameter.

Metric & Standard Bolt & Screw Size Chart: M2, M4, M5, M6, M8, M10 (4)

How do I know the screw size?

Identifying sizes can be difficult if you don't know how to read them. They are presented alphanumericallyCode, which is difficult to understand if you are not familiar with it. Codes like "1/8-10 x 4/6", "M5-0.4 x 15" and "4-30 x 0.10" may seem overwhelming and meaningless at the same time, but they are the most important pieces of information.

What's the point of knowing these things when you can get into the hardware?save on computerand ask the seller for help? Well, there isn't always someone available to help you. Sometimes they don't know much about it. You may receive incorrect or inaccurate information. When it comes to complicated things like sizes, it helps to know the basics. It can save you from buying the wrong type, resulting in unnecessary expense and wasted time and effort. It can even lead to a failed project.

  1. Step 1: Identify the first number of the size

    The first number is the largest diameter measurement of the thread. For example, a 4-30 x .10 is .112 inches in diameter. That's because .060 + (4 x .013) = .112 inches.

    If it is greater than ten, it is expressed as a fraction of an inch. For example, a 1/8-10 x 4/6 is 1/8 inch in diameter.

    If you see the letter M, it means the measurement is in millimeters. For example, M5-0.4 x 10 has an outside diameter of 5mm.

  2. Step 2: Reading the second number

    The second number expresses the number of threads per unit distance between these threads. You can also refer to it as the thread pitch. If you have a 4-30 x .10, the threads per inch (TPI) is 30.

    In the metric system, threads are expressed in millimeters per thread. An M5-0.4 x 15 is threaded every 0.4mm.

  3. Step 3: Reading the third number

    The third number is typically the one after the x and indicates the length of the screw. You measure them all from the bottom of the head to the top. The only exception to the rule are countersunk screws that sit flush on the surface. You should measure this guy from crown to tip. An M5-0.4x15 is 15mm in length.
Metric & Standard Bolt & Screw Size Chart: M2, M4, M5, M6, M8, M10 (5)

What do the numbers in the screw sizes mean?

If you do DIY often, you are one of the most popular itemswith screws. It is available in several sizes, which you can see on the packaging. Finding the right size can be a daunting task if you are unfamiliar with the imperial or metric system. A conversion table would be useful if you frequently convert between these two systems.

Several companies list metric and imperial sizes on the packaging, which is helpful for most consumers. The challenge often comes when buying online. Most retailers do not list both system sizes on the product page. Why? This makes the product page too long.

Imperial sizes

The gauge shows the diameter. A larger number means a larger diameter, while a smaller number means a smaller diameter. For example, a number 3 is less than a number 11.

Gauge sizes have no direct correlation to actual head size. When measuring the length of a countersunk screw, start at the top of the head and work your way down to the shank. On the other hand, for other species, start from the bottom of the head to the stem. Thetrack width and lengthdetermine size.

(Video) How Metric Bolts are Measured

To calculate the strength and head size, you can use the following formula.

Gauge = (head diameter in sixteenths of an inch x 2) – 2

Metric sizes

In general, the metric system is easier to understand. It may take additional time to adjust if you are already familiar with the Imperial system. Instead of using gauges to express diameter, the metric system uses millimeters. On the other hand, it still uses millimeters to measure length.

The gauge(imperial) is approximately the head size in millimeters (metric). However, there is no correlation or scientific explanation here.

Metric & Standard Bolt & Screw Size Chart: M2, M4, M5, M6, M8, M10 (6)

Metric system

The metric system was based on the meter, a system of measurement that originated inFrance in the 1970s. When we take the length of a screw we use meters.

For the most accurate length, measure in millimeters from wherescrew headsits to the top. They don't always measure from the top of the head. It depends on where the head would sit on the surface. Use a ruler or tape measure to get the most accurate measurement.

Here are some points to keep in mind when determining length:

  • Screw heads lie differently on surfaces. If the head is flat, it's most likely a flush fit. Otherwise there is a bump.
  • For flat heads, measure from tip to tip to get length.
  • For round heads, measure from the top to the bottom of the head. The rounded head protrudes from the surface, which should not be taken into account when measuring.
  • For all other types that are not countersunk, measure from the flat bottom to the top.

Once you have the length, it's time to get the diameter. Use millimeters to measure from one side of a thread to the other. If the packaging has dimensions given in the metric system, the first digit indicates the diameter. For example, 4.0 means the screw is 4 millimeters (mm) in diameter.

Lastly you need to measure the distance from one thread to the other. It is also known as pitch. In the metric system we use the pitch instead of the thread pitch. To get this final measurement, use a ruler or tape measure. In most cases the pitch would only be less than 1mm. It is given with a decimal point of mm.

In summary, the diameter is listed first before the length. For example, 4.0 x 50 means the screw is 4mm in diameter and 50mm in length.


The default system is also known as thatImperial System. It was introduced in the British Weights and Measures Act 1824. It evolved through a series of changes in that law. For some time the imperial system was theStandardmeasuring system. By the late 20th century, several countries had adopted the metric system. Currently, Canada and the United Kingdom are countries that still use the imperial system of units.

The imperial system uses inches to determine the length from the tip to the seat of the head and the diameter. The measurement should start where the head rests.

Metric & Standard Bolt & Screw Size Chart: M2, M4, M5, M6, M8, M10 (7)

When determining length in inches, consider the following:

  • Take the length of a flat head from the top to the top of the head.
  • For round heads that are not countersunk, measure from the flat bottom to the top.
  • For round head countersunks, start measuring where the countersunk and oval top meet in the center. Simply put, the oval top would be resting on the surface.
  • For flatheads that are recessed, measure from the tip to the top of the head.

Measure the diameter by measuring the width of the thread in fractions of an inch with a tape measure or ruler. AThe measurement number or fraction of an inch represents the diameterin the imperial system.

  • AThe gauge number represents a fraction of an inchIn diameter. To know the diameter, you must refer to a gauge guide to adjust the gauge by a fraction of an inch.
  • For example, a #0 gauge is 1/16 inch in diameter. A #1 gauge is 5/64 inch and a #2 gauge is 3/32 inch.

Finally, count the threads in an inch to get the thread spacing value. To get an accurate measurement, place the screw next to a tape measure or ruler and count the number of threads. Thread counts in the imperial system range from 35 to 40 threads per inch. Thread pitch and thread spacing mean the same thing, so don't confuse the two.

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shopping guide

Now that we've covered some of the basics, it's time to walk you through what you need to know. Finding the right type and specs holds the materials together well.

The type

Metric & Standard Bolt & Screw Size Chart: M2, M4, M5, M6, M8, M10 (8)

Depending on the application, they come in different shapes and sizes. Here are some of the most common.

cement board

Thecement boardType is fully threaded and secures backing plate to subfloor or wall stud. The coating prevents corrosion from mortar and moisture. You can use it in metal and wood.

Metric & Standard Bolt & Screw Size Chart: M2, M4, M5, M6, M8, M10 (9)


Awood screwhas a pointed tip that aids in wood-to-wood attachment. One part has coarse threads while the other is an unthreaded shank. It helps to join pieces of wood together. A common type is the round head pan head.


Deck screws are e.gfencingand decks, but they can also be used for similar outdoor projects. Composite decks have fine threads and a small head. On the other hand, wooden decks have an unthreaded shaft and a coarsely threaded portion.


Drywall screws are for interior finishing projects, specifically for securingdrywall. Fine thread drywall works best with metal studs, while coarse thread works with wood studs. Note that drywall cannot be supportedtileand cement board.

Metric & Standard Bolt & Screw Size Chart: M2, M4, M5, M6, M8, M10 (10)


We use a lag screw to attach the componentshandle a heavy load. It has a hex head so you need a socket and a ratchet or oneKeyto secure it in place.

structural wood

Timber screws have an unthreaded shank and coarse threads. Structural wood furniture may appear similar to wood, but it is more durable.


Secure self-tapping screwssheet. They are fully threaded and available for use with self-drilling tips and pre-drilled holes.

Metric & Standard Bolt & Screw Size Chart: M2, M4, M5, M6, M8, M10 (11)


Machine screws are fully threaded that you can use to fastenmetal parts together. The two main types are cylinder head bolts and socket sets. The has a cylindrical, raised hexagonal head, while the latter is headless.

Metric & Standard Bolt & Screw Size Chart: M2, M4, M5, M6, M8, M10 (12)


You can use one of several materials, e.g. B. drywall or sheet metal. Wood and plastic are also good options.


To fasten concrete you need a concrete screw. Some require you to pre-drill while others are self-tapping. This allows you to drill directly into the surface without pre-drilling.

drive types

Phillips and slotted drives are the two main types. Some are a combination that works for both types.

There's also the Allen drive, which has a six-sided bushing. The square drive (Robertson drive) and the star drive (Torx) have a head that minimizes slipping out.


Fine thread screws are best used with pre-drilled holes. The closer spacing between these threads allows for a firm hold. However, removing or installing would take longer.

Coarse threads have a larger distance between the threads. We often use it on softer materials like drywall or wood. It's easy to install and remove.

Here's a good resource. Make sure you get the correct screw length, thread diameter, and screw threads for your project. We also have a resource on Phillips head options.

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What is the screw size number?

This is an indication of how big it is, as well as the threads per inch. You can gather a lot of information from this number.

How big is a #8 screw?

4.2mm in diameter.

What size is an M3 screw?

3.0mm in diameter.

What size is an M2 screw?

2.0mm in diameter.

Metric & Standard Bolt & Screw Size Chart: M2, M4, M5, M6, M8, M10 (13)

Needed time:5 minutes.

How do I recognize a screw size?

  1. Place the screw on a flat surface.

    You want the whole thing to lay flat, which means the head needs to rest off the edge of a table or other surface.

    (Video) How to Measure Screws & Bolts - US & Metric Sizing | Fasteners 101

  2. On the axis you want to place the ruler.

    Start with the first thread that gets number zero.

  3. Within 1 inch of the screw, start counting the thread gaps.
  4. Find the TPI by dividing the thread gaps by the 1 inch length.

    If there are 6 thread gaps, divide 1 inch by 6, resulting in thread gaps of 0.1667 inch.

  5. Since it lays flat, measure across the diameter.

    The outermost part is where you want to measure. If you take measurements on a worn one, you will get inaccurate results.


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