Thread Pitch Chart: Metric Coarse & Fine Table (Free PDF)

This table apply to metric screws and ISO 261 (ISO metric screw thread). For each size, it gives the coarse pitch from size M1 to M64.

To find the coarse pitch: Look in the Size column for the diameter of your thread. Then move across the row. Millimeters is shown on the table as the pitch. It is also shown in inches. This is the number of threads per inch, which is the equivalent. It is the distance that a caliper should of measure across ten thread crests.

So if a bolt is simply given the diameter, then coarse is assumed. Unless it says otherwise, it’s an M12 with a 1.75 pitch; it’s M12 x 1.75.

Thread pitch is the distance between adjacent thread crests, measured parallel to the axis of the thread. The unit is the millimetre. It is NOT the number of threads to an inch (TPI). Thread pitch is NEVER given in TPI, and the term applies to metric threads. Only included so that those who know it may use TPI to help them convert gauges. The value is 25.4 ÷ pitch.

Spanning over 10 threads is a useful tool to help with measurement. Set your calipers over eleven threads and read across, it will include ten complete pitch intervals. Compare your reading against this column. Use it to verify a pitch without a gauge.

The size choice column from the ISO 261 table indicates the preferred order of sizes from that standard. Select 1st choice diameters if possible. Only select a second choice size if needed. Only select special design sizes such as M9 and M11 when needed.

The selected column from ISO 262 indicates if the size exists in that standard. This is the abbreviated commercial nuts, bolts, screws, and studs standard. A "Yes" indicates it is an easy-to-find, off-the-shelf fastener. A "No" indicates it is not commonly found, although the size has been standardized. That would apply to a size like M2.2, M4.5, M9, or M11.

This table is intentionaly incomplete. ISO 261 has no coarse pitch for M5.5, M15, M17, M25, M26, M28, M32, M35, M38, M40, M50, M55, M58 and M62. It is only in the fine pitch series. See the fine pitch table below.

Also, be aware of the near miss imperial size trap. A 3/8-16 UNC bolt closely resembles an M10 x 1.5 bolt. Over ten threads, their difference is more near 0.9 mm. If you mix them, they will either strip or seize together.

These are ISO general purpose metric threads.

This table is limited to ISO general purpose metric threads (M profile and 60 degree flank angle). This is not applicable to pipe threads such as NPT or BSP. This is not applicable to Japanese JIS small-head flange bolts or trapezoidal threads such as lead screws. For those diameters, JIS pitches corresponds to ISO, but the standards themselves does not match.

ISO 261 extends beyond M64 all the way up to M300. Beyond M64, there is no coarse series. The range just goes from 1.5 to 8mm with fine pitches only.

Here’s a table of all the standard fine pitches assigned by ISO 261 for each metric diameter (M1 to M64) and placed next to their corresponding coarse pitch for comparison.

Each value is a genuine standard thread you’re likely to encounter in the field. They’ve listed them largest first in the Fine pitch options column to look at after determining your size. Because a fine thread always has its pitch included when it’s written, if you see a part noted as M10 x 1.25 then it’s a fine pitch part; whereas just M10 means it’s the coarse pitch (in this case being 1.5 mm).

This brings us to the fine selection column in the ISO 262, which narrows down the list of available pitches to those used on commercially available fasteners. This is where you’ll find the fine threads that are available as off-the-shelf bolts and nuts, things like M8 x 1, M10 x 1.25, M12 x 1.5, M12 x 1.25.

All other fine threads outside this column (for example M30 x 1.5 or M20 x 1) are technicially ISO threads. However, they are typically limited to hydraulic fittings, spindles, adjusting rings and machine design. Most require a special order or will need to has the thread cut to suit.

The traps is flagged in the Note column. There are also some fine-only diameter (no coarse pitch defined), such as: M5.5, M15, M17, M25, M26, M28, M32, M35, M38, M40, M50, M55, M58, and M62. These are mainly used for machine spindles and bearing retention.

The ISO 261 reserves M14 x 1.25 for spark plug threads, hence you’ll see that size in a cylinder head, maybe, but hardly on a bolt. The 3 mm pitch appears in parentheses in the standard for M30 and M33. This pitch should of be avoided if possible, because it conflicts with the 3 mm coarse pitch of M24 and M27 found in toolboxes and stores.

Maybe you select a fine thread instead of a coarse one. It will have a smaller helix angle (a shallower angle). This helps it resist loosening from vibration better and adjust to finer tolerances. It also exits leaving a greater minor diameter, making the fastener nominally the same size but slightly stronger in tension.

The downside: fine threads is harder to install and require more turns. They are also more likely to foul from damage or dirt, and they can cross-thread. General purpose fastening still defaults to coarse, while fine justifies itself on thin-wall parts, engines and wheels, as well as sensors.

You always need to measure the pitch with calipers or a gauge before assuming it’s coarse. Once you do, you'll find that M12 nuts is available in 1, 1.25, 1.5, and 1.75 mm pitches. They will all start turning on the wrong bolt for a turn or two until they jam.

Assuming your measurement isn’t on this list at all, then you might want to guess that it’s an imperial thread and look up the TPI conversion table below.

The table above converts threads per inch (TPI) to millimetre pitch to compare with the metric thread tables above. It’s just straight arithmetic since there are 25.4 mm per inch. That means pitch in mm = 25.4 ÷ TPI.

Look up the TPI of an imperial screw, or look at your gauge and it will say how many threads is per inch; you can use that to find the real pitch in both inches and millimetres.

These two columns is for settling any disputes about what is being identified, not to allow substituting one for another. The Difference column indicate whether the closest matching metric pitch has a slightly coarser (negative) or finer (positive) pitch compared to the imperial thread.

Even a tiny .006 mm per-thread difference will add up over the length of thread engagement, and the flanks might be off angle as well. UN and ISO metric threads both has 60 degree angles, while BSW, BSP and BSC has 55 degree angles.

Don’t assume you can get away with running a metric nut on an imperial bolt just because it fits smoothly on the first few turns; don’t do that. You should of known that.

You will most often find that particular count listed in the Where this TPI appears column. That’s for NPT and BSP pipe threads (at 11.5, 14, 19, and 28 TPI), UNF and UNC fastener sizes, the ever-popular UN series with a constant pitch, and even British cycle thread, at 26 TPI.

Note: The chart intentionaly only goes as far as to identify the pitch. If you want complete Unified thread dimension including diameters, tap drills, and TPI counts per size, check out our UNC and UNF thread chart, which digs deep in the imperial side of things.

If none of the metric table values match what you measure for that strange fastener’s pitch, then divide 25.4 by that value (in mm). If the answer come up within approximately 2 percent of a whole number in this table, then you've got yourself some imperial thread.

Here, a measured 1.59 mm pitch converts to 25.4 / 1.59 = 16.0. Yes sirree, it’s 16 TPI, probably 3/8-16 UNC, which looks like M10 x 1.5 but isn’t.

Here’s a table showing you the combination of pitches and metric threads most commonaly found on motorbikes and cars. You’ll most often use it to look up thread pitch size. Locate the part in the Application section. Look up its thread size (standard designator), the mm pitch, and if it’s fine or coarse for that size.

Fine pitch is what you’ll find in almost every case here. A reason manufacturers opt for fine pitch are because it seals better and resists vibration.

M10 x 1.0, M12 x 1.25, M14 x 1.25, and M18 x 1.5 is the four spark plug threads. That's fixed in ISO 28741 which also lists those figures; they're shared among all major plug makers. Once you know that table, then you can identify what size plug from just its thread.

Even ISO 261 has a note reserving the 1.25 mm pitch at 14 mm diameter for spark plugs. The 18 mm plugs have the same M18 x 1.5 thread as oxygen and lambda sensor do. That is why plug thread chasers are also sold for sensor bosses.

The largest trap on the list is wheel lug threads. Across manufacturers you’ll find M12 x 1.25, M12 x 1.5, M14 x 1.25 and M14 x 1.5 all existing side by side. You can start a lug nut that is one size off by hand, but when under torque, it will strip the stud. Always check the thread before transferring lug nuts between vehicles.

The pitches here are confirmed against a lug nut manufacturer's reference chart. Older American trailers and vehicles still has their imperial studs in 7/16-20, 1/2-20 and 9/16-18. Those go by their full dimensions in our thread chart for UNC and UNF.

The Japanese motorcycle chassis standard for fine pitch is 10 mm and up. Common engine mount and other brake hardware sizes is M10 x 1.25. M6 and M8 hardware uses ISO coarse pitches of 1.0 and 1.25.

European bikes commonly have M10 x 1.5 coarse threads. A mix of different standards are common on the same bike. That’s exactly what makes the table of identifications below useful. Don’t presume size. Go by measurement first.

The table lists common uses but doesn't imply any such application is guaranteed for this particular model year. The manufacturers frequently alter sensor and stud threads between generations.

Consider the table your shortlist of possible contenders. Check one with a known good nut or a gauge. Only Bosch sensor value is shown. Clamping torques should of been checked in the vehicle's service manual.

Instead of one interval, it’s more like ten to find the pitch. Count out eleven crests on the bolt, starting with the crest where you placed the rest of the caliper jaw. Then close the other jaw on the eleventh crest. Doing this multiply the accuracy of your reading by ten.

Next, you’ll see the measurement in the Span over 10 pitches column. Look for the number there, and if it is a clean match, that's the metric pitch. Which size use that pitch is in the final column as either fine or coarse. This is what makes the difference between a 1.25 mm pitch versus a 1.27 mm pitch, for example.

The closest imperial TPI and imperial span shows possible imperial matches.

The Difference column shows the gap between those two readings over ten pitches.

UNSAFE: Rows of 0.7 and 0.8 mm are unsafe. Over a span of ten pitches, there’s only 0.06 mm between these pitches and UNF No.8 at 36 TPI and 32 TPI hardware. In such instances, you’ll have to rely on diameter.

A No.8 screw has a diameter of 4.17mm while an M4 bolt measures 4.0 mm. A No.10 screw measures 4.83 mm where an M5 bolt is 5.0 mm. Automotive mishaps are most likely when using 1.25 pitch threads instead of 20 TPI, or 1.5 pitch threads different than 16 TPI.

Is it an internal thread? Thread pitch gauge wins faster.

Calipers cannot get to internal threads. The gauge comes in handy here too. Fan out the leaves and push each candidate into the thread against the light. Accept only the leaf that seat without a hint of light at any crest.

Leaves stamped with metric show the pitch in mm. Gauges cover common pitches from 0.25 through 6 mm. Leaves stamped imperial show TPI. Common ranges goes from 4 to 62.

If a leaf fits at one end but rocks at the other, you have a tapered, damaged, or stretched thread. There is no indication this is a near-standard pitch.

But two additional checks confirm the ID. One is measuring the outside diameter. With a metric bolt, you are right under nominal size. An M10 thread has an OD of around 9.8 to 9.97 mm. An imperial diameter lands on fractions of 25.4 mm. A 3/8 in thread is about 9.4 mm.

Then you attempt to fit the candidate with a known nut of that size. You should of be able to turn the nut by hand all the way along. It shouldn't bind. If it binds after a couple of turns, then the pitch is incorrect. The diameter might have been correct but the pitch wasn't.

This presumes a fairly undamaged 60 degree thread. Damaged threads, paint, or rolled bumps will move the position of the crests. Take the span reading on the cleanest stretch. Repeat the reading in a second position.

Nothing matching here? Check the fine pitch table for fine only. Also check the TPI conversion table. Next, check the pipe threads. The diameters of pipe threads does not match either system.