Metric Screw Size Chart - Guide with Complete Dimensions (2024)

Whether you’re buying screws online or in-store, if you don’t know how to read screw callouts, you’ll probably end up getting the wrong size.

Although it might seem hard to understand screw sizes, it’s actually a lot simpler than what you think.

Once you figure out the meaning of each number found in screw callouts, you’ll find that reading callouts and screw size charts is a piece of cake.

You also might be familiar with reading imperial screw callouts.

However, you can find some screw packages that are available in metric sizes only.

So, it’s important to familiarize yourself with both of them.

In this article, you’ll find all the information you need to read metric screw sizes easily. We also included an easy-to-follow metric screw size chart.

Let’s get started!

Terms You Must Know to Read Metric Screw Size Charts

If you’re used to using the imperial screw sizes, reading screw sizes in mm might be confusing to you.

Metric callouts look different from imperial ones. Thus, metric screw size charts will have different info than what is provided in imperial charts.

So, we’ll be starting by explaining how to read metric screw callouts first. This will help you use our metric screw size chart that is included further in the article.

How to Read Metric Screw Sizes?

A metric callout on a screw package usually looks like this: M6 × 1.00 × 25. So, what does this even mean?

Typically, screw callouts contain three numbers whether for imperial or metric ones. Metric callouts usually contain:

1. Screw Diameter

Unlike imperial callouts, the metric screw size callouts always start with the letter M followed by a number. This number is the screw diameter.

The screw diameter or major diameter is the outside diameter of the screw. In other terms, it’s the diameter of the screw shank.

Don’t get it confused with the US gauge. Just because they’re both written as the first numbers in callouts, doesn’t mean that they’re the same thing.

It’s really complicated to understand the correlation between metric screw diameter and gauge.

In this system, screw sizes are often referred to by a number followed by the symbol “G” or “ga” (for gauge). For instance, a #6 screw has a larger diameter than a #4 screw.

It’s important to note that screw gauges may vary depending on the specific standards used in different regions or industries.

2. Screw Pitch

The screw pitch is represented by the second number you see in the callout. It represents the distance between each thread on the screw in mm.

You can find that the screw pitch isn’t included in imperial callouts. Instead, you’ll find the number of threads per inch (TPI).

In metric screw sizes, you usually find the screw pitch represented in the second column.

You can also find two pitch columns. One for coarse screws and the other for fine screws.

A coarse screw is a screw with a low number of threads along the screw. While a fine screw has a high number of threads.

So, of course, the pitch number will be different between the two.

In our metric screw size chart, we provide the pitch for both coarse and fine threads.

3. Screw Length

The screw length is the third and final number you find in metric callouts. It’s measured differently depending on the type of the screw head.

For countersinking screws, their length is measured from the top of their heads to their tips.

This is because they’re designed to be installed flat or flush with the surface.

On the other hand, non-countersinking threads are designed so that their heads remain above the surface.

So, the screw length in this case is measured from beneath the head to the tip.

To understand how to choose the right screw length for your project, check out this video:

Example: Reading Metric Machine Screw Sizes

To make sure that you understand how to read metric callouts on screw packages, let’s try to read this metric machine screw callout:

M3 × 1.25 × 30

This callout means:

The first number after the letter M is the screw diameter which equals 3 mm
The second number is the screw’s pitch which equals 1.25 mm
The third and final number is the screw’s length which equals 30 mm

Since we also talked about imperial screw callouts, let’s read this screw thread callout as well:

#6 x 1 x 1/2″

We have here:

The first number represents the US gauge number, which represents the diameter of the screw shaft. It’s essentially a measurement of the thickness of the screw’s body.
The second number represents the number of threads per inch which is 1
The third and final number is the screw’s length which equals ½ inch

Pro-tip, you might find some imperial callouts that contain only two numbers. These two numbers are the gauge number and screw length.

What about the thread per inch number? In this case, it means that the screw has the standard number of threads.

The Only Metric Screw Size Chart You’ll Need

In our metric screw size chart, you’ll find all the information you need to buy the right size of screws for your project. Our chart includes:

Screw diameter
Screw pitch for both coarse and fine screws
Tap drill for both coarse and fine screws
Finally, clearance drill

Metric Screw Size	Metric Screw Diameter	Screw Pitch (Coarse)	Tap Drill (Coarse)	Screw Pitch (Fine)	Tap Drill (Fine)	Clearance Drill
M1	1	0.25	0.75	0.2	0.8	1.2
M1.2	1.2	0.25	0.95	0.2	1	1.4
M1.4	1.4	0.3	1.1	0.2	1.2	2
M1.6	1.6	0.35	1.25	0.2	1.4	1.8
M1.8	1.8	0.35	1.45	0.2	1.6	2
M2	2	0.4	1.6	0.25	1.75	2.4
M2.5	2.5	0.45	2	0.35	2.1	2.9
M3	3	0.5	2.5	0.35	2.6	3.4
M3.5	3.5	0.6	2.9	0.35	3.1	3.9
M4	4	0.7	3.3	0.5	3.5	4.5
M5	5	0.8	4.2	0.5	4.5	5.5
M6	6	1	5	0.75	5.2	6.6
M7	7	1	6	0.75	6.2	8
M8	8	1.25	6.8	0.75 or 1	7.2	9
M9	9	1.25	7.75	0.75 or 1	8.25 or 8
M10	10	1.5	8.5	1 or 1.15	8 or 8.75	12
M11	11	1.5	9.5	1 or 1.25	10 or 9.75
M12	12	1.75	10.2	1.25 or 1.5	10.75 or 10.5	14
M14	14	2	12	1.5	12.5	16
M16	16	2	14	1.5	14.5	18
M17	17			1 or 1.5	16 or 15.5
M18	18	2.5	15.5	1. 5 or 2	16.5 or 16	20
M19	19			1	18
M20	20	2.5	17.5	1.5	18.5 or 18	22
M24	24	3	21	1.5 or 2	22.5 or 22	26
M25	25			1.5 or 2	23.5 or 23
M27	27	3	24	2	25	30
M28	28			1.5	26.5
M28	28			2	26
M30	30	3.5	26.5	2 or 3	28 or 27	33
M32	32			1. 5 or 2	30.5 or 30
M33	33	3.5	29.5	2	31	36
M35	35			2 or 3	33 or 32
M36	36	4	32	2 or 3	34 or 33	39
M38	38			1.5 or 2	36.5 or 36
M39	39	4	35	2 or 3	37 or 36	42
M40	40			1.5 or 3	38.5 or 37
M42	42	4.5	37.5	3 or 4	39 or 38	45
M45	45	4.5	40.5	3 or 4	42 or 41	48
M48	48	5	43	3 or 4	45 or 44	52
M50	50			2 or 3	48 or 47
M52	52	5	47	3 or 4	49 or 48	56
M56	56	5.5	50.5	2 or 4	54 or 52	62
M60	60	5.5	54.5	4	56	65

FAQs

Here are some common questions people tend to ask about metric screw size charts:

1. What Does the Letter “M” Mean on Screw Packages?

The letter “M” on screw packages refers to the metric system (ISO). So, when you see it at the beginning of a callout, it means that the measurements are in mm.

2. What Is the Shank of a Screw?

The shank is the part of the screw that lies beneath the screw’s head. It can be threaded all the way to the tip, partially-threaded, or not threaded at all.

3. What Is the Difference Between Metric Machine Screw Sizes and Wood Screw Sizes?

There isn’t a noticeable difference between machine and wood screw sizes. However, the difference is in the physical characteristics.

You can usually spot these with your eye, but you’ll definitely know when you try to fit one with another (we’ve all been there!).

Machine screws always have an all-threaded shank with finer threads.

Despite being smaller, they’re much stronger than other types of screws.

To Sum Up

Here you have it, our metric screw size chart that includes screw sizes in mm up to M60.

As you can see metric callouts and metric screw size charts are much easier to read and understand than imperial.

You only need to find the values for the screw’s diameter, pitch, and length.

Now, you can go and purchase your screw package with all confidence. Good luck!