Thread Chart (Metric Threads) - Major and Minor Diameters

Metric Thread Chart

There are various thread types and sizes to choose from these days.  Occasionally, you need to know the dimensions associated with those threads, so we're developing posts like this one to make it easy for you.

Below you will find a quick reference chart and a more extensive list of dimensions for metric threads.  The chart below will focus on the major diameters for external threads and the minor diameters for internal threads.  We've included the image below to show these areas better.

major diameter of threadsmajor diameter of threads
minor diameter of threadsminor diameter of threads


 Simple Thread Designation  Thread Designation Pitch (MM)

Basic Major Diameter

(External Threads)

Basic Minor Diameter

(Internal Threads)

M1 M1x0.25 0.25 0.982 0.729
M2 M2x0.4 0.4 1.981 1.567
M3 M3x0.5 0.5 2.980 2.459
M4 M4x0.7 0.7 3.978 3.242
M5 M5x0.8 0.8 4.976 4.134
M6 M6x1 1 5.974 4.917
M7 M7x1 1 6.974 5.917
M8 M8x1.25 1.25 7.972 6.647
M9 M9x1.25 1.25 8.972 7.647
M10 M10x1.5 1.5 9.968 8.376
M12 M12x1.75 1.75 11.970 10.106
M14 M14x2 2 13.960 11.835
M16 M16x2 2 15.960 13.835
M18 M18x2.5 2.5 17.960 15.294
M20 M20x2.5 2.5 19.960 17.294
M22 M22x2.5 2.5 21.960 19.294
 M24 M24x3 3 23.950 20.752
M27 M27x3 3 26.950 23.752
M30 M30x3.5 3.5 29.950 26.211
M33 M33x3.5 3.5 32.970 29.211
M36 M36x4 4 35.940 31.670
M39 M39x4 4 38.940 34.670
M42 M42x4.5 4.5 41.940 37.129
M45 M45x4.5 4.5 44.940 40.129
M48 M48x5 5 47.930 42.587
M52 M52x5 5 51.930 46.587
M56 M56x5.5 5.5 55.930 50.046

metric thread chartmetric thread chart

Metric vs. Standard

The major difference between metric and standard is in how threads are specified. When it comes to fasteners that use threading, an extra measurement called "thread pitch" is added after the diameter measurement. Examples of standard fasteners would be 1/4-20, 1/4-28, and 3/8-16. Examples of metric fasteners would be M6x1, M12x1.75, and M18x2.5.

Standard thread pitch is how many threads there are per inch. For example, a 1/4-20 thread means the diameter of the nut or bolt is 1/4 inch and that there are 20 threads per inch.

Metric thread pitch is the distance between the threads. For example, an M18x2.5 thread means the diameter of the nut or bolt is 18 millimeters and that there are 2.5mm between the threads.


Using Chart for Choosing Masking Caps & Plugs

There are various reasons you may have needed to reference the chart, so we hope it was helpful for you! Here at Echo, we use it to help powder coaters, e-coaters, anodizers, and platers find the correct sized cap or plug for their specific thread size. So, here are a few tips in case you ever need it. 

Metric Bolts | Cap It

When you need to mask off a metric threaded bolt, you'll most likely need a silicone or EPDM rubber masking cap.

The simple version of finding the right size cap is that we suggest finding one with an ID (inside diameter) 0.4 to 0.8 millimeters smaller than the Major Diameter of the thread you're masking off.  For submersion-based processes, like e-coating,  you'll want the cap to fit tighter.

Sizing a masking capSizing a masking cap

Metric Holes | Plug It

For tapered plugs, you'll want to closely match the minor diameter to the middle diameter of the plug (see graphic). So if your hole is 6.35 millimeters in diameter, you will want the middle diameter of the plug (shown in red in the illustration here) to be right around 6.35 millimeters. If it's not exact, seat the plug deeper in the hole. When installing these plugs, you push them in and then turn them to get a better seal.

You will want to choose a plug 0.8 millimeters bigger than the hole for pull plugs to achieve a snug fit.

sizing a tapered plugsizing a tapered plug

About Echo Engineering

Echo Engineering has provided masking solutions to industrial finishers for well over 50 years. We specialize in not only standard catalog options, like powder coating tapes, caps, and plugs, but also in designing, engineering, and manufacturing custom solutions for some of the most prominent metal finishing lines in the world. Because of that, we are frequently working closely with paint lines to help them find ways of masking off threaded holes and bolts.

If you need a masking solution or have a question you'd like to ask us, please fill out the form below, and we will get back to you as soon as possible!

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We'd love to help you solve your company's biggest production challenges.

Let us know what project you're working on and how our team can help you create the best solution!

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