Thread Chart (Metric Threads) - Major and Minor Diameters
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By
Lee Lechner - May 18, 2022
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.
THREAD CHART (METRIC 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 |
Download Full Metric Thread Size Chart
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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.
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.
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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