Watch these two
7/16″ and 9/16″
The hex cap screw and the hex nut take different wrenches: 5/8″ and 11/16″ for 7/16, 13/16″ and 7/8″ for 9/16. Every other size matches.
Heavy hex
One size up
Heavy hex bolts and nuts are 1/8″ bigger across the flats than standard hex. That includes A325 and A490 structural bolts and 2H nuts.
Metric
ISO vs DIN
Older DIN bolts and nuts use a different wrench on M10, M12, M14 and M22. If a 16 mm doesn’t fit an M10, try a 17.
Sockets
6 or 12 point
Both fit the same across-flats size. A 6-point socket grips the flats and is the better choice for tight or rounded heads.
Inch bolts and nuts
Source: ASME B18.2.1 (hex cap screws, heavy hex bolts) and B18.2.2 (hex and heavy hex nuts), basic width across flats. Jam nuts take the same wrench as the full nut of the same type. Heavy hex bolts start at 1/2″; below that, heavy hex comes as nuts only. — means that style isn’t standard at that size.
1/4″ 5/16″ 3/8″ 7/16″ 1/2″ 9/16″ 5/8″ 3/4″ 7/8″ 1″ 1-1/8″ 1-1/4″ 1-3/8″ 1-1/2″ 1-3/4″ 2″ 2-1/4″ 2-1/2″ 2-3/4″ 3″ 3-1/4″ 3-1/2″ 3-3/4″ 4″
| Size | Hex cap screwwrench | Hex nut& jam nut | Heavy hexbolt & nut |
|---|---|---|---|
| 1/4″ | 7/16″0.4375″ · ≈ 11.1 mm | 7/16″0.4375″ · ≈ 11.1 mm | 1/2″0.5000″ · ≈ 12.7 mmnut only |
| 5/16″ | 1/2″0.5000″ · ≈ 12.7 mm | 1/2″0.5000″ · ≈ 12.7 mm | 9/16″0.5625″ · ≈ 14.3 mmnut only |
| 3/8″ | 9/16″0.5625″ · ≈ 14.3 mm | 9/16″0.5625″ · ≈ 14.3 mm | 11/16″0.6875″ · ≈ 17.5 mmnut only |
| 7/16″ | 5/8″0.6250″ · ≈ 15.9 mm | 11/16″0.6875″ · ≈ 17.5 mmnut differs from screw | 3/4″0.7500″ · ≈ 19.0 mmnut only |
| 1/2″ | 3/4″0.7500″ · ≈ 19.0 mm | 3/4″0.7500″ · ≈ 19.0 mm | 7/8″0.8750″ · ≈ 22.2 mm |
| 9/16″ | 13/16″0.8125″ · ≈ 20.6 mm | 7/8″0.8750″ · ≈ 22.2 mmnut differs from screw | 15/16″0.9375″ · ≈ 23.8 mm |
| 5/8″ | 15/16″0.9375″ · ≈ 23.8 mm | 15/16″0.9375″ · ≈ 23.8 mm | 1-1/16″1.0625″ · ≈ 27.0 mm |
| 3/4″ | 1-1/8″1.1250″ · ≈ 28.6 mm | 1-1/8″1.1250″ · ≈ 28.6 mm | 1-1/4″1.2500″ · ≈ 31.8 mm |
| 7/8″ | 1-5/16″1.3125″ · ≈ 33.3 mm | 1-5/16″1.3125″ · ≈ 33.3 mm | 1-7/16″1.4375″ · ≈ 36.5 mm |
| 1″ | 1-1/2″1.5000″ · ≈ 38.1 mm | 1-1/2″1.5000″ · ≈ 38.1 mm | 1-5/8″1.6250″ · ≈ 41.3 mm |
| 1-1/8″ | 1-11/16″1.6875″ · ≈ 42.9 mm | 1-11/16″1.6875″ · ≈ 42.9 mm | 1-13/16″1.8125″ · ≈ 46.0 mm |
| 1-1/4″ | 1-7/8″1.8750″ · ≈ 47.6 mm | 1-7/8″1.8750″ · ≈ 47.6 mm | 2″2.0000″ · ≈ 50.8 mm |
| 1-3/8″ | 2-1/16″2.0625″ · ≈ 52.4 mm | 2-1/16″2.0625″ · ≈ 52.4 mm | 2-3/16″2.1875″ · ≈ 55.6 mm |
| 1-1/2″ | 2-1/4″2.2500″ · ≈ 57.1 mm | 2-1/4″2.2500″ · ≈ 57.1 mm | 2-3/8″2.3750″ · ≈ 60.3 mm |
| 1-3/4″ | 2-5/8″2.6250″ · ≈ 66.7 mm | — | 2-3/4″2.7500″ · ≈ 69.8 mm |
| 2″ | 3″3.0000″ · ≈ 76.2 mm | — | 3-1/8″3.1250″ · ≈ 79.4 mm |
| 2-1/4″ | 3-3/8″3.3750″ · ≈ 85.7 mm | — | 3-1/2″3.5000″ · ≈ 88.9 mm |
| 2-1/2″ | 3-3/4″3.7500″ · ≈ 95.2 mm | — | 3-7/8″3.8750″ · ≈ 98.4 mm |
| 2-3/4″ | 4-1/8″4.1250″ · ≈ 104.8 mm | — | 4-1/4″4.2500″ · ≈ 107.9 mm |
| 3″ | 4-1/2″4.5000″ · ≈ 114.3 mm | — | 4-5/8″4.6250″ · ≈ 117.5 mm |
| 3-1/4″ | — | — | 5″5.0000″ · ≈ 127.0 mm |
| 3-1/2″ | — | — | 5-3/8″5.3750″ · ≈ 136.5 mm |
| 3-3/4″ | — | — | 5-3/4″5.7500″ · ≈ 146.0 mm |
| 4″ | — | — | 6-1/8″6.1250″ · ≈ 155.6 mm |
Metric bolts and nuts
Source: ISO 4014 / 4017 bolts and ISO 4032 nuts; DIN 931 / 933 bolts and DIN 934 nuts; EN 14399-4 (HV) structural bolts and nuts. The ISO and DIN columns only differ on M10, M12, M14 and M22.
| Size | ISObolt & nut | DINbolt & nut | StructuralHV, 10.9 |
|---|---|---|---|
| M3 | 5.5mm≈ 0.217″ | 5.5mm≈ 0.217″ | — |
| M4 | 7mm≈ 0.276″ | 7mm≈ 0.276″ | — |
| M5 | 8mm≈ 0.315″ | 8mm≈ 0.315″ | — |
| M6 | 10mm≈ 0.394″ | 10mm≈ 0.394″ | — |
| M8 | 13mm≈ 0.512″ | 13mm≈ 0.512″ | — |
| M10 | 16mm≈ 0.630″ | 17mm≈ 0.669″differs from ISO | — |
| M12 | 18mm≈ 0.709″ | 19mm≈ 0.748″differs from ISO | 22mm≈ 0.866″ |
| M14 | 21mm≈ 0.827″ | 22mm≈ 0.866″differs from ISO | — |
| M16 | 24mm≈ 0.945″ | 24mm≈ 0.945″ | 27mm≈ 1.063″ |
| M18 | 27mm≈ 1.063″ | 27mm≈ 1.063″ | — |
| M20 | 30mm≈ 1.181″ | 30mm≈ 1.181″ | 32mm≈ 1.260″ |
| M22 | 34mm≈ 1.339″ | 32mm≈ 1.260″differs from ISO | 36mm≈ 1.417″ |
| M24 | 36mm≈ 1.417″ | 36mm≈ 1.417″ | 41mm≈ 1.614″ |
| M27 | 41mm≈ 1.614″ | 41mm≈ 1.614″ | 46mm≈ 1.811″ |
| M30 | 46mm≈ 1.811″ | 46mm≈ 1.811″ | 50mm≈ 1.969″ |
| M33 | 50mm≈ 1.969″ | 50mm≈ 1.969″ | — |
| M36 | 55mm≈ 2.165″ | 55mm≈ 2.165″ | 60mm≈ 2.362″ |
| M39 | 60mm≈ 2.362″ | 60mm≈ 2.362″ | — |
| M42 | 65mm≈ 2.559″ | 65mm≈ 2.559″ | — |
| M45 | 70mm≈ 2.756″ | 70mm≈ 2.756″ | — |
| M48 | 75mm≈ 2.953″ | 75mm≈ 2.953″ | — |
| M52 | 80mm≈ 3.150″ | 80mm≈ 3.150″ | — |
| M56 | 85mm≈ 3.346″ | 85mm≈ 3.346″ | — |
| M60 | 90mm≈ 3.543″ | 90mm≈ 3.543″ | — |
| M64 | 95mm≈ 3.740″ | 95mm≈ 3.740″ | — |
Sizes are the nominal (basic) width across flats. Finished heads run a few thousandths under, so the listed wrench is the one that fits. Reference information only — verify against the current published standard before use. Need thread sizes too? See the inch and metric thread pitch charts.