Wrench Size Chart for Metric Bolts (M6–M64)
The wrench size (across flats) of a hex bolt determines the matching socket or spanner size. The table below lists the across-flats size and the coarse thread pitch for metric bolts from M6 to M64 — per current standard DIN EN ISO 4014/4017/4032 and, where it differs, the older value per DIN 931/934.
Across-flats size & thread pitch (metric coarse thread)
| Thread | Pitch (mm) | A/F current (mm) DIN EN ISO 4014/4017 | A/F old (mm) DIN 931/934 |
|---|---|---|---|
| M6 | 1.00 | 10 | — |
| M8 | 1.25 | 13 | — |
| M10 | 1.50 | 16 | 17 |
| M12 | 1.75 | 18 | 19 |
| M14 | 2.00 | 21 | 22 |
| M16 | 2.00 | 24 | — |
| M18 | 2.50 | 27 | — |
| M20 | 2.50 | 30 | — |
| M22 | 2.50 | 34 | 32 |
| M24 | 3.00 | 36 | — |
| M27 | 3.00 | 41 | — |
| M30 | 3.50 | 46 | — |
| M33 | 3.50 | 50 | — |
| M36 | 4.00 | 55 | — |
| M39 | 4.00 | 60 | — |
| M42 | 4.50 | 65 | — |
| M45 | 4.50 | 70 | — |
| M48 | 5.00 | 75 | — |
| M52 | 5.00 | 80 | — |
| M56 | 5.50 | 85 | — |
| M64 | 6.00 | 95 | — |
A/F = width across flats. The "old" column is shown only where the historic DIN 931 value differs from today's ISO value — on older plant, check both.
Why there is no universal torque table
Tightening torque cannot be read from bolt size alone. It depends on strength class (e.g. 8.8, 10.9, B7), friction and lubrication (friction coefficient µ) and the required preload — in torque-controlled tightening up to ~90 % of the torque is lost to friction. For pressurised flange joints, torque or preload is therefore calculated per joint (EN 1591-1, ASME PCC-1) and documented.
More precise than torque control is bolt tensioning (hydraulic axial bolt elongation): preload scatter typically ±5–10 % instead of ±25–30 %. Real HSOS project values give the order of magnitude: vessel flange with 1¾″ bolts → 4,800 Nm; HP pre-heater with M72 → 10,200 Nm.
Bolting to standard — calculated and documented
HSOS performs controlled bolting and bolt tensioning on flange joints across Europe — with bolt-load calculation, calibrated equipment and a joint report for every connection.