Every thread number that the calculators on this site ask for, in one place: pitch and TPI, major, pitch, and minor diameters, the tensile stress area behind every strength number, and the tap drill that starts the internal thread. Metric M2–M48 coarse and fine; unified #0 to 1-1/2″ UNC and UNF — computed from the basic 60° thread form so the tables stay self-consistent to the last decimal.
Diameters follow the basic thread form: pitch diameter d₂ = d − 0.6495·p, minor diameter d₁ = d − 1.0825·p. The tensile stress area uses the ISO 68-1 formula in the next section. Tap drill is the common 75%-thread approximation d − p.
| Size | Pitch p (mm) | Major d (mm) | Pitch dia d₂ (mm) | Minor d₁ (mm) | As (mm²) | Fine pitch (mm) | Tap drill (mm) |
|---|---|---|---|---|---|---|---|
| M2 | 0.4 | 2 | 1.74 | 1.567 | 2.1 | — | 1.6 |
| M2.5 | 0.45 | 2.5 | 2.208 | 2.013 | 3.4 | — | 2.05 |
| M3 | 0.5 | 3 | 2.675 | 2.459 | 5 | — | 2.5 |
| M4 | 0.7 | 4 | 3.545 | 3.242 | 8.8 | — | 3.3 |
| M5 | 0.8 | 5 | 4.48 | 4.134 | 14.2 | — | 4.2 |
| M6 | 1 | 6 | 5.351 | 4.918 | 20.1 | 0.75 | 5 |
| M8 | 1.25 | 8 | 7.188 | 6.647 | 36.6 | 1 | 6.75 |
| M10 | 1.5 | 10 | 9.026 | 8.376 | 58 | 1.25 | 8.5 |
| M12 | 1.75 | 12 | 10.863 | 10.106 | 84.3 | 1.25 | 10.25 |
| M14 | 2 | 14 | 12.701 | 11.835 | 115.4 | 1.5 | 12 |
| M16 | 2 | 16 | 14.701 | 13.835 | 156.7 | 1.5 | 14 |
| M20 | 2.5 | 20 | 18.376 | 17.294 | 244.8 | 1.5 | 17.5 |
| M24 | 3 | 24 | 22.052 | 20.753 | 352.5 | 2 | 21 |
| M30 | 3.5 | 30 | 27.727 | 26.211 | 560.6 | 2 | 26.5 |
| M36 | 4 | 36 | 33.402 | 31.67 | 816.7 | 3 | 32 |
| M42 | 4.5 | 42 | 39.077 | 37.129 | 1120.9 | 3 | 37.5 |
| M48 | 5 | 48 | 44.752 | 42.587 | 1473.1 | 3 | 43 |
Fine pitch columns show the ISO 261 fine series where a standard variant exists — fine tap drill ≈ d − fine pitch. Basic diameters are unrounded theoretical values; actual parts carry ISO 965 tolerance classes (6H internal / 6g external is the common fit) on top of these numbers.
Unified geometry follows the same 60° form per inch: pitch diameter = D − 0.6495/n, minor diameter = D − 1.0825/n, with n the threads per inch. Stress areas are shown in mm² for direct comparison with the metric table; multiply by 0.00155 to read in². Tap drill approximates the 75%-thread value D − 1/n.
| Size | TPI | Major D (in) | Pitch dia (in) | Minor (in) | As (mm²) | UNF TPI | Tap drill (in) |
|---|---|---|---|---|---|---|---|
| #0 | 48 | 0.06 | 0.0465 | 0.0374 | 0.8 | — | 0.039 |
| #1 | 40 | 0.073 | 0.0568 | 0.0459 | 1.2 | — | 0.048 |
| #2 | 32 | 0.086 | 0.0657 | 0.0522 | 1.6 | — | 0.055 |
| #4 | 40 | 0.112 | 0.0958 | 0.0849 | 3.9 | — | 0.087 |
| #6 | 32 | 0.138 | 0.1177 | 0.1042 | 5.9 | — | 0.107 |
| #8 | 32 | 0.164 | 0.1437 | 0.1302 | 9 | — | 0.133 |
| #10 | 24 | 0.19 | 0.1629 | 0.1449 | 11.3 | 32 | 0.148 |
| 1/4" | 20 | 0.25 | 0.2175 | 0.1959 | 20.5 | 28 | 0.2 |
| 5/16" | 18 | 0.3125 | 0.2764 | 0.2524 | 33.8 | 24 | 0.257 |
| 3/8" | 16 | 0.375 | 0.3344 | 0.3073 | 50 | 24 | 0.313 |
| 7/16" | 14 | 0.4375 | 0.3911 | 0.3602 | 68.6 | 20 | 0.366 |
| 1/2" | 13 | 0.5 | 0.45 | 0.4167 | 91.5 | 20 | 0.423 |
| 9/16" | 12 | 0.5625 | 0.5084 | 0.4723 | 117.4 | 18 | 0.479 |
| 5/8" | 11 | 0.625 | 0.566 | 0.5266 | 145.8 | 18 | 0.534 |
| 3/4" | 10 | 0.75 | 0.6851 | 0.6418 | 215.8 | 16 | 0.65 |
| 7/8" | 9 | 0.875 | 0.8028 | 0.7547 | 297.9 | 14 | 0.764 |
| 1" | 8 | 1 | 0.9188 | 0.8647 | 390.8 | 12 | 0.875 |
| 1-1/8" | 7 | 1.125 | 1.0322 | 0.9704 | 492.4 | 12 | 0.982 |
| 1-1/4" | 7 | 1.25 | 1.1572 | 1.0954 | 625.2 | 12 | 1.107 |
| 1-3/8" | 6 | 1.375 | 1.2668 | 1.1946 | 745.1 | 12 | 1.208 |
| 1-1/2" | 6 | 1.5 | 1.3918 | 1.3196 | 906.6 | 12 | 1.333 |
Tap drill values are computed approximations, not the letter/number drill chart — for example 1/4-20 wants a #7 drill (0.201 in), which the formula reproduces at 0.200. Choose the nearest standard drill; the labeled chart on the homepage’s tap-drill section lists the conventional lettered and numbered selections.
Measure across ten threads, divide by tenPhoto: UnsplashWhy compute instead of copy?
Printed charts round, drop fine series, and stop at the sizes their editors guessed you’d need. The tables above are generated live from the same formulas the site’s calculators run — so the As in a row here is bit-identical to the As inside the strength check, and the table extends to the whole standard ladder without typos.
A metric callout like M10×1.5 states the nominal diameter and the pitch in one breath; a unified callout like 1/4-20 UNC states the diameter in inches and the threads per inch. Everything else in the tables derives from those two numbers through the 60° thread form — the same geometry in both systems, just anchored differently.
As = 0.7854 · (d − 0.9382·p)²
As = 0.7854 · (d − 0.9743/n)² (unified)
tensile stress area — the number every strength calculation on this site uses
p = 25.4 / TPI, and TPI = 25.4 / p. The reciprocal pair across millimeters and inches is the single most useful conversion in mixed-unit shops: an 8 TPI thread is a 3.175 mm pitch, and an M12 coarse thread at 1.75 mm is 14.5 TPI — close to, but never exactly, a unified pitch.
Major is the crest diameter — the nominal. The basic pitch diameter sits where the thread flanks would meet a sharp V: d − 0.6495·p. The basic minor is the root: d − 1.0825·p. These are the sharp-V basics; real parts truncate and tolerance them, which is what the 6g/6H classes control.
A pitch gauge reads it directly. Without one, count crests over a ruler: across ten threads is the reliable span, because a single-thread measurement at 1.5 mm pitch is inside most rulers' error. Unified threads are friendlier — crests per inch is a straight count.
Three wires of known diameter seated in the V-grooves, micrometer across them, and the standard wire correction added. Thread micrometers and optical comparators do the same job faster; all three verify the number the tolerance class promises.
This page is the input sheet for the rest of the toolset, and each column maps to a specific calculator downstream. Knowing which number goes where is the difference between a lookup and an engineering habit.
The tensile stress area column is what the bolt size calculator walks against a required area, and what the preload check multiplies by the grade's yield. Any capacity number in kN or lbf on this site started as an As from this table.
The torque calculator uses the series to pick As; the thread engagement calculator takes pitch to compute the pitch diameter that sets minimum engagement depth in a tapped hole.
Before any thread exists, the drill decides its strength. The d − p rule lands near the 75% thread engagement most tapped holes want — enough strength without breaking taps in tough material.
Go/no-go gauges and three-wire measurements verify the manufactured thread against the basic diameters plus its tolerance class. The table's basic values are the anchor the tolerances reference.
Use this bolt thread pitch chart alongside its companions: the hex bolt & nut dimensions chart covers the head and wrench sizes outside the thread, and the clearance hole chart covers the hole the bolt passes through. For calculations, start at the bolt torque calculator on our homepage or browse every tool on the all calculators page — the As values here are the exact ones those tools use.
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