Metric Thread Pitch Chart: Coarse vs Fine (M1-M24)
How metric pitches are named
A metric callout carries two numbers: the diameter after the M, and the pitch in millimetres between adjacent thread crests. M10 x 1.25 means a 10 mm thread with crests 1.25 mm apart. When the pitch is omitted — “M10”, or just M10x40 where the 40 is the length — the coarse pitch is always implied: 1.5 mm for M10. That convention is written into ISO 261 and its Chinese twin GB/T 193-2003, which define every valid diameter-pitch combination.
Fine pitch must be specified explicitly, every time. A drawing that says “M12x1.5” and a drawing that says “M12” order two different parts that will strip each other’s threads if mixed.
Metric thread pitch chart: coarse vs fine, M1 to M24
The coarse column is the single default pitch for each diameter. The fine column lists the standard fine options in ISO 261 / GB/T 193 order. Tap drill (for cutting internal threads) follows the drill-size rule that works across both series: drill = diameter − pitch, rounded to the nearest drill.
| Size | Coarse pitch (mm) | Tap drill, coarse (mm) | Fine pitch options (mm) | Tap drill, first fine (mm) |
|---|---|---|---|---|
| M1 | 0.25 | 0.75 | — | — |
| M1.2 | 0.25 | 0.95 | — | — |
| M1.4 | 0.30 | 1.10 | — | — |
| M1.6 | 0.35 | 1.25 | 0.2 | 1.4 |
| M2 | 0.40 | 1.60 | 0.25 | 1.75 |
| M2.5 | 0.45 | 2.05 | 0.35 | 2.15 |
| M3 | 0.50 | 2.50 | 0.35 | 2.65 |
| M3.5 | 0.60 | 2.90 | — | — |
| M4 | 0.70 | 3.30 | 0.50 | 3.50 |
| M5 | 0.80 | 4.20 | 0.50 | 4.50 |
| M6 | 1.00 | 5.00 | 0.75, 0.5 | 5.25 |
| M8 | 1.25 | 6.75 | 1.0, 0.75 | 7.00 |
| M10 | 1.50 | 8.50 | 1.25, 1.0 | 8.75 |
| M12 | 1.75 | 10.25 | 1.5, 1.25, 1.0 | 10.50 |
| M14 | 2.00 | 12.00 | 1.5 | 12.50 |
| M16 | 2.00 | 14.00 | 1.5, 1.0, 0.75 | 14.50 |
| M18 | 2.50 | 15.50 | 2.0, 1.5 | 16.00 |
| M20 | 2.50 | 17.50 | 2.0, 1.5 | 18.00 |
| M22 | 2.50 | 19.50 | 2.0, 1.5 | 20.00 |
| M24 | 3.00 | 21.00 | 2.0, 1.5 | 22.00 |
Two habits worth keeping: check the fine column before assuming “M12x1.5” — some drawings mean M12x1.25, the other common fine option; and below M1.6 there is no fine series at all, which is why the smallest sizes in our micro screws range are all coarse by definition.
When fine pitch actually earns its place
Fine thread is not a “premium” version of coarse — it trades ease of assembly for four specific advantages:
- Vibration resistance. A finer pitch has a smaller helix angle, so the inclined-plane wedge that backs the nut off is shallower. In jostled assemblies without prevailing-torque nuts, fine threads stay put longer.
- More tensile strength from the same bolt. The core diameter of an M10x1.25 is larger than that of an M10x1.5 — the deeper thread of coarse pitch cuts further into the shank. Fine pitch quietly carries more load per millimetre of shank.
- Thin walls. Fine pitch needs less engagement depth to develop full strength, so it is the default on thin-wall housings, tubes and sheet-metal bosses.
- Precise adjustment. One turn of an M12x1.0 moves 1.0 mm against 1.75 mm for coarse — fine pitch is the language of setting screws, spindles and anything adjusted with a dial.
What fine pitch costs you
The trade-offs are real, and most of them show up at the bench rather than on the drawing: less flank depth means fewer stripping cycles before the thread gives out; 6g-class fine threads demand cleaner tapping and tighter torque control; and the small helix angle that stops loosening also makes galling nastier once it starts — stainless pairs are the classic case, covered in our galling guide. Fine pitch also engages more turns for the same clamp length, so assembly takes marginally longer on long bolts.
How the fine-pitch shelf is actually stocked
This is the part charts never tell you: which fine pitches a real warehouse carries, and in what. Across this store, 868 part numbers are labelled fine thread against 3,020 coarse — fine is roughly one shelf in five, and it is not evenly spread:
| Diameter | Fine part numbers | Diameter | Fine part numbers |
|---|---|---|---|
| M12 | 217 | M16 | 50 |
| M10 | 170 | M20 | 21 |
| M8 | 96 | M18 | 20 |
| M6 | 60 | M5 | 22 |
| M14 | 52 | M4 / M3 | 19 / 14 |
Where the standard families sit:
| Standard | Fine part numbers | What it is |
|---|---|---|
| DIN 912 socket head | 202 | Fine-pitch cap screws — the largest fine shelf |
| DIN 933 hex bolt, full thread | 116 | Fine-pitch hex bolts |
| DIN 913 set screw | 108 | Cone-point adjustment screws |
| DIN 6334 long nut | 72 | Threaded rod couplers, mostly fine |
| DIN 916 set screw | 61 | Cup-point adjustment screws |
| GB 5786 hex bolt | 45 | The Chinese fine-pitch twin of GB/T 5783 — see the GB 5786 page |
The material mix tells the same story from another angle: 588 of the fine part numbers are 304 stainless, but the next tiers are 40Cr (124) and SCM435 alloy steel (61) — heat-treated steels that go into adjusted, high-vibration joints. Fine pitch is where the strength-grade materials live. On diameter labels, our store marks fine pitches explicitly (M12-1.5, M10-1.25, M8-1.0), so a BOM that specifies pitch survives a keyword search intact.
If your application is coarse-threaded fastening by design, the working assumptions are different — DIN 933 vs DIN 931 covers thread length, and the DIN 912 page lists fine and coarse matrices side by side for cap screws.
How to measure an unknown pitch
Three ways, in descending order of reliability: a thread pitch gauge (match the serrated blade, read the number); calipers across 10 crests, divided by 10 — better resolution than a single-pitch measurement on small sizes; and for the desperate, count turns over a known length. One trap worth naming: an M10x1.0 and M10x1.25 will start together for a turn or two and feel “almost right”, then bind. If a nut suddenly stops mid-run, stop turning — forcing it strips the flanks, and the parts are scrap.
Ordering note
Every pitch listed above is priced per piece in USD with no minimum order, shipped from our own warehouse within 24–48 hours. If the pitch you need is not on the shelf, send the drawing — fine and special pitches are a standard quote for us. For the pan-head end of the coarse range, start at the GB 818 machine screw guide; for grade designations behind the alloy steels mentioned above, see A2-70 vs grade 8.8.
FAQ
What is the coarse pitch of M10?
1.5 mm. Coarse is the default: “M10” with no pitch stated always means M10x1.5. The fine options are 1.25, 1.0 and 0.75 mm, and they must be written out explicitly.
What is the difference between M12x1.5 and M12x1.75?
M12x1.75 is the coarse pitch — the default M12. M12x1.5 is the most common fine option; 1.25 and 1.0 mm also exist. The two do not interchange: a 1.5 nut on a 1.75 bolt will jam after one or two turns and destroy both threads if forced.
How do I calculate the tap drill size?
Drill diameter = thread diameter minus pitch. M8x1.25 taps from a 6.75 mm drill; M8x1.0 from a 7.0 mm drill. It is the same formula in both series — only the pitch you subtract changes.
Is fine thread stronger than coarse thread?
In tensile strength, yes: the shallower thread leaves a larger core diameter, so a fine-pitch bolt of the same size and grade carries more tension. In shear and stripping resistance, coarse is more forgiving. Fine pitch also resists loosening better because its helix angle is smaller.
Why is fine thread used for vibration-prone joints?
The smaller helix angle of a fine thread gives the nut a shallower “ramp” to slide down, so axial jostling converts less of its energy into rotation. For extreme vibration, fine pitch is combined with prevailing-torque or flanged hardware rather than relied on alone.
Do you stock fine-pitch screws below M4?
Below M4 the standard series has no fine options for most diameters, and our fine shelf reflects that: the smallest fine-pitch part numbers start at M3, while everything from M0.9 to M2 in the micro screws range is coarse.
How many fine-pitch parts do you stock?
868 part numbers are labelled fine thread, concentrated in M12 (217), M10 (170) and M8 (96), across DIN 912, DIN 933, DIN 913/916 set screws, DIN 6334 nuts and GB 5786 hex bolts — all priced per piece with no minimum order.