MechPilotISO 273 clearance holes for bolts and screws, M1.6 to M64
The diameter of the clearance hole for a metric bolt or screw, in three series: fine, medium and coarse.
| Thread | Fine series (mm), H12 | Medium series (mm), H13 | Coarse series (mm), H14 |
|---|---|---|---|
| M1.6 | 1.7 | 1.8 | 2 |
| M1.8 | 2 | 2.1 | 2.2 |
| M2 | 2.2 | 2.4 | 2.6 |
| M2.5 | 2.7 | 2.9 | 3.1 |
| M3 | 3.2 | 3.4 | 3.6 |
| M3.5 | 3.7 | 3.9 | 4.2 |
| M4 | 4.3 | 4.5 | 4.8 |
| M4.5 | 4.8 | 5 | 5.3 |
| M5 | 5.3 | 5.5 | 5.8 |
| M6 | 6.4 | 6.6 | 7 |
| M7 | 7.4 | 7.6 | 8 |
| M8 | 8.4 | 9 | 10 |
| M10 | 10.5 | 11 | 12 |
| M12 | 13 | 13.5 | 14.5 |
| M14 | 15 | 15.5 | 16.5 |
| M16 | 17 | 17.5 | 18.5 |
| M18 | 19 | 20 | 21 |
| M20 | 21 | 22 | 24 |
| M22 | 23 | 24 | 26 |
| M24 | 25 | 26 | 28 |
| M27 | 28 | 30 | 32 |
| M30 | 31 | 33 | 35 |
| M33 | 34 | 36 | 38 |
| M36 | 37 | 39 | 42 |
| M39 | 40 | 42 | 45 |
| M42 | 43 | 45 | 48 |
| M45 | 46 | 48 | 52 |
| M48 | 50 | 52 | 56 |
| M52 | 54 | 56 | 62 |
| M56 | 58 | 62 | 66 |
| M60 | 62 | 66 | 70 |
| M64 | 66 | 70 | 74 |
ISO 273:1979, clause 2, table: thread diameter d and clearance hole d_h, series fine / medium / coarse
Tolerance classes: ISO 273:1979, clause 2, note below the table: tolerance fields given for information only, for use where it is desirable to specify tolerances
Notes from the data file
- Default series: medium. ISO 273:1979 does not name a default series; medium is the usual choice for general-purpose bolted joints and is MechPilot's own choice. The user can switch to fine or coarse per hole.
- ISO 273:1979, clause 1: the values are for general-purpose applications and come from bearing-area calculations with the ISO bolt and nut product standards; clearance holes for special applications are chosen from the design requirements.
- ISO 273:1979, clause 2, last note: where the edge of the hole would interfere with the underhead fillet of the bolt, a chamfer is recommended.
Source and verification
- Standard
- ISO 273:1979 Fasteners - Clearance holes for bolts and screws, clause 2 (Dimensions, table of clearance hole diameters d_h for the fine, medium and coarse series)
- Verification
primary(the standard’s own text was seen)- Verified from
- https://law.resource.org/pub/in/bis/S01/is.1821.1987.pdf (IS 1821:1987, identical with ISO 273:1979: clause 1 scope, clause 2 table and notes; read from the rendered page on 2026-10-22)
- Verification notes
- Every diameter below was read from the table in ISO 273:1979 clause 2 (IS 1821:1987, an identical adoption). The national foreword uses the decimal point; the table itself uses the decimal comma.
- ISO 273:1979 lists thread diameters from 1 mm to 150 mm. MechPilot stores M1.6 to M64; M1, M1.2, M1.4 and M68 to M150 are in the standard but not stored here (not needed by the kernel yet).
- Data file
library/holes/iso-273.json
Values that could not be checked against the standard are left out and listed in docs/to-verify.md. Check the standard itself before you rely on a value for production, and report any mistake on GitHub. to-verify.md · Issues