ISO 965 / ISO 262 / ISO 724
ISO metric thread sizes, coarse and fine pitches, tap drill diameters and the tolerance class to write on a drawing.
ISO 965 / ISO 262 / ISO 724 · See source catalogue · unit: mm
The tap drill column is the nominal rule of thumb of the nominal diameter minus the pitch. Confirm the thread series and the edition against the drawing.
| Thread designation | Coarse pitch P (mm) | Fine pitch P (mm) | Tap drill Ø ≈ D−P (mm) | Major Ø D (mm) | Minor Ø D1 (mm) | Tolerance class |
|---|---|---|---|---|---|---|
| M1 × 0.25 | 0.25 | 0.2 | 0.75 | 1 | 0.729 | 6g |
| M1.2 × 0.25 | 0.25 | 0.2 | 0.95 | 1.2 | 0.929 | 6g |
| M1.4 × 0.3 | 0.3 | 0.2 | 1.1 | 1.4 | 1.075 | 6g |
| M1.6 × 0.35 | 0.35 | 0.2 | 1.25 | 1.6 | 1.221 | 6g |
| M2 × 0.4 | 0.4 | 0.25 | 1.6 | 2 | 1.567 | 6g |
| M2.5 × 0.45 | 0.45 | 0.35 | 2.05 | 2.5 | 2.013 | 6g |
| M3 × 0.5 | 0.5 | 0.35 | 2.5 | 3 | 2.459 | 6g |
| M3.5 × 0.6 | 0.6 | 0.35 | 2.9 | 3.5 | 2.851 | 6g |
| M4 × 0.7 | 0.7 | 0.5 | 3.3 | 4 | 3.242 | 6g |
| M5 × 0.8 | 0.8 | 0.5 | 4.2 | 5 | 4.134 | 6g |
| M6 × 1 | 1 | 0.75 | 5 | 6 | 4.918 | 6g |
| M8 × 1.25 | 1.25 | 1 | 6.75 | 8 | 6.647 | 6g |
| M10 × 1.5 | 1.5 | 1.25 | 8.5 | 10 | 8.376 | 6g |
| M12 × 1.75 | 1.75 | 1.5 | 10.25 | 12 | 10.106 | 6g |
| M16 × 2 | 2 | 1.5 | 14 | 16 | 13.835 | 6g |
| M20 × 2.5 | 2.5 | 2 | 17.5 | 20 | 17.294 | 6g |
| M24 × 3 | 3 | 2 | 21 | 24 | 20.753 | 6g |
| M30 × 3.5 | 3.5 | 2.5 | 26.5 | 30 | 26.211 | 6g |
| M36 × 4 | 4 | 3 | 32 | 36 | 31.67 | 6g |
| M42 × 4.5 | 4.5 | 3.5 | 37.5 | 42 | 37.129 | 6g |
| M48 × 5 | 5 | 4 | 43 | 48 | 42.587 | 6g |
| M56 × 5.5 | 5.5 | 4 | 50.5 | 56 | 50.046 | 6g |
| M64 × 6 | 6 | 5 | 58 | 64 | 57.505 | 6g |
Metric threads follow ISO 965 for the coarse series, ISO 262 for the fine series and ISO 273 for the tap drill sizes. The tap drill column is the nominal rule of thumb of the nominal diameter minus the pitch. Never leave the thread system implicit on a drawing that also carries inch dimensions.
Reference source
ISO 965 / ISO 262 / ISO 724
Call out the nominal diameter and the pitch, for example M10 x 1.5, followed by the tolerance class, for example M10 x 1.5 - 6H. For a hole, use the thread designation with a note such as 6H and depth. For a bolt hole that is not tapped, specify the tap drill diameter and the thread class.
The coarse pitch is the standard default and gives a stronger thread with a larger thread profile. A fine pitch gives a larger minor diameter, so it has a larger tensile stress area, and it needs a smaller axial adjustment, but it is more sensitive to damage and to cross-threading.
The rule of thumb is the nominal diameter minus the pitch. For M10 x 1.5 the tap drill is 8.5 mm, and for M6 x 1.0 it is 5.0 mm. The published tap drill sizes are sometimes a fraction larger to reduce the risk of the tap breaking, so use the value from the tap supplier when the hole is critical.
A thread relief is needed where the turned shoulder comes close to the thread, because the thread run-out leaves an incomplete profile. Standard practice is to keep at least one full pitch of clearance between the end of the thread and the shoulder, and to undercut where space is tight.
6 is the tolerance grade, which fixes the width of the tolerance band, and H is the position of the band relative to the nominal size. For an internal thread, H means the hole is never below the nominal size. The matching external class for a normal clearance fit is 6g, while 6e and 6f give a smaller clearance.
For a normal bolted joint use 6H for the tapped hole and 6g for the bolt, which is the default in ISO 965. Use 6H only when the hole must be assembled without a clearance, and specify a tighter class such as 4H6g only when the joint has to be precise or the environment is aggressive.
They do, and the result is a part that does not assemble. Always state the thread system explicitly, and add a note such as metric ISO 965 wherever inch threads appear in the same drawing set. Watch out for a nominal diameter of 12.7 mm, which is exactly half an inch and is a common source of confusion.
Send the drawing and the requirements to Evefab’s engineering team. We reply with manufacturability feedback, not just a price.
