🔧 Metric Thread Pitch Calculator
Calculate thread pitch, minor diameter, pitch diameter, tap drill size, and thread depth for any metric thread.
| Thread Size | Pitch (mm) | Major Dia. (mm) | Pitch Dia. (mm) | Minor Dia. (mm) | Tap Drill (mm) | Thread Depth (mm) |
|---|---|---|---|---|---|---|
| M3 | 0.5 | 3.000 | 2.675 | 2.459 | 2.5 | 0.325 |
| M4 | 0.7 | 4.000 | 3.545 | 3.242 | 3.3 | 0.455 |
| M5 | 0.8 | 5.000 | 4.480 | 4.134 | 4.2 | 0.520 |
| M6 | 1.0 | 6.000 | 5.350 | 4.917 | 5.0 | 0.650 |
| M8 | 1.25 | 8.000 | 7.188 | 6.647 | 6.8 | 0.812 |
| M10 | 1.5 | 10.000 | 9.026 | 8.376 | 8.5 | 0.974 |
| M12 | 1.75 | 12.000 | 10.863 | 10.106 | 10.2 | 1.137 |
| M14 | 2.0 | 14.000 | 12.701 | 11.835 | 12.0 | 1.299 |
| M16 | 2.0 | 16.000 | 14.701 | 13.835 | 14.0 | 1.299 |
| M20 | 2.5 | 20.000 | 18.376 | 17.294 | 17.5 | 1.624 |
| M24 | 3.0 | 24.000 | 22.051 | 20.752 | 21.0 | 1.949 |
| M30 | 3.5 | 30.000 | 27.727 | 26.211 | 26.5 | 2.273 |
| M36 | 4.0 | 36.000 | 33.402 | 31.670 | 32.0 | 2.598 |
| M42 | 4.5 | 42.000 | 39.077 | 37.129 | 37.5 | 2.923 |
| M48 | 5.0 | 48.000 | 44.752 | 42.587 | 43.0 | 3.248 |
| Material | SFM Range | M6 RPM | M10 RPM | M16 RPM | Lubricant | Hardness (HB) |
|---|---|---|---|---|---|---|
| Aluminum | 200–400 | 2100–4200 | 1200–2500 | 750–1550 | Cutting oil / WD-40 | 65–150 |
| Mild Steel | 60–120 | 630–1270 | 360–730 | 225–450 | Sulfurized cutting oil | 120–180 |
| Stainless Steel | 30–60 | 315–635 | 180–365 | 110–230 | Tapping fluid (heavy) | 150–300 |
| Brass / Bronze | 150–300 | 1590–3180 | 910–1820 | 570–1140 | Dry or light oil | 60–150 |
| Cast Iron | 50–80 | 530–850 | 300–480 | 190–300 | Dry (blow chips) | 150–250 |
| Titanium | 20–40 | 210–420 | 120–240 | 75–150 | Chlorinated tapping fluid | 200–350 |
| Plastic / Nylon | 300–600 | 3180–6360 | 1820–3640 | 1140–2280 | Dry | N/A |
| Copper | 100–200 | 1060–2120 | 610–1210 | 380–760 | Light cutting oil | 35–100 |
| Thread | Pitch (mm) | 75% Thread Drill | 50% Thread Drill | Clearance Drill | ISO Tolerance | Notes |
|---|---|---|---|---|---|---|
| M3 | 0.5 | 2.50 mm | 2.75 mm | 3.20 mm | 6H | Standard nut |
| M4 | 0.7 | 3.30 mm | 3.65 mm | 4.30 mm | 6H | Standard nut |
| M5 | 0.8 | 4.20 mm | 4.60 mm | 5.30 mm | 6H | Standard nut |
| M6 | 1.0 | 5.00 mm | 5.50 mm | 6.40 mm | 6H | Very common |
| M8 | 1.25 | 6.80 mm | 7.40 mm | 8.40 mm | 6H | Very common |
| M10 | 1.5 | 8.50 mm | 9.25 mm | 10.50 mm | 6H | Common bolt |
| M12 | 1.75 | 10.20 mm | 11.13 mm | 13.00 mm | 6H | Common bolt |
| M16 | 2.0 | 14.00 mm | 15.00 mm | 17.00 mm | 6H | Structural |
| M20 | 2.5 | 17.50 mm | 18.75 mm | 21.00 mm | 6H | Heavy bolt |
| M24 | 3.0 | 21.00 mm | 22.50 mm | 25.00 mm | 6H | Heavy bolt |
The Metric Thread Pitch in the metric system simply shows the distance, that one measures in millimeters between two peaks of the thread. At the base everything deals with that. If you look at metric thread in ISO-style for screws, you will notice the letter M, followed by the main diameter and then the pitch, both values in millimeters, separated by a stroke or by “x”. For instance M8-1.25 shows you everything, what matters about the size and the right pitch here.
On metric screws the pitch always appears after the diameter, with hyphen or little “x” as separator.
Metric Thread Pitch and How to Measure It
The values of pitch work the opposite way regarding the fineness of the thread. Smaller pitches give more tihgt thread with narrower space between it, while big pitches make the thread rough and more spread out. Among the common metric threads you find M5 x 0.8, M6 x 1, M8 x 1.25 and M10 x 1.5.
Basically the pitch decides how far the screw or bolt moves during one full turn. Here the point however, metric threads do not split only into “coarse” and “fine” groups, as some believe. For every diameter there is a standard pitch, plus some options for separate uses, that need denser or broader spacing.
The tie between Metric Thread Pitch and the imperial system for threads in inch deserves attention. Rather than the SAE-system, that counts threads each inch, the metric way is more direct, because it measures the real distance between the threads. Like this 28 TPI-thread almost matches with 1.25 mm pitch metric.
Also, the coarse type of M4-thread has around 0.7 mm between one thread and the next.
The checking of metric threads is not too hard. One measures the distance over four threads, that covers seven millimeters of the screw length. For precise size ratings, special tools help a lot; for example thread gauges or optical tools.
Also the calculation of depth is easy: you multiply the pitch by 0.866 and receive the depth of the thread.
The gauges for Metric Thread Pitch truly help in that task. They are made up of metal books with sheets, that look like little saws stacked together. Every page bears teeth, that match a certain pitch, and the relevant measure is printed directly on it.
To use it, you line up the teeth with the thread of the screw, until the peaks and valleys perfectly match. When it fits, you simply read the visible number. Using imperial gauges on metric thread does not help at all, so separate gauges for every system are needed.
Most tap and dye sets come with gauges for metric and SAE, that show pitches in millimeters or threads each inch according too the system.
The diameter of the screw itself gives clues about what happens. Metric screws usually come in sizes of 5, 6, 8, 10 and 12 mm. After you find the diameter, finding the Metric Thread Pitch becomes easy work.
The markings printed on the head of the screw can also show, whether it is metric orimperial type.
