Current Metric Bolt Sizes - Black Bolts, Countersunk and Preloaded (HSFG)
Black Bolts
Bolt dimensions for black bolts (non-preloaded bolts) in accordance with BS EN ISO 4014, 4017 (Bolts) and BS ISO 4032 (Nuts) are given in the table below:
| Bolt dimensions | Nut dimensions | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Reference | Nominal Diameter (mm) | Pitch (mm) | Unthreaded Area (mm²) | Stress Area (mm²) | Width Across Flats - min (mm) | Width Across Flats - max (mm) | Width Across Corners - max (mm) | Head Thickness (mm) | Width Across Flats - min (mm) | Width Across Flats - max (mm) | Width Across Corners - max (mm) | Hole Diameter (mm) |
| M10 | 10 | 1.5 | 78.5 | 58 | 15.57 | 16 | 17.59 | 6.4 | 15.73 | 16 | 17.77 | 11 |
| M12 | 12 | 1.75 | 113 | 84.3 | 17.57 | 18 | 19.95 | 7.5 | 17.73 | 18 | 20.03 | 13 |
| M16 | 16 | 2 | 201 | 157 | 23.16 | 24 | 26.17 | 10 | 23.67 | 24 | 26.75 | 18 |
| M20 | 20 | 2.5 | 314 | 245 | 29.16 | 30 | 32.95 | 12.5 | 29.16 | 30 | 32.95 | 22 |
| M22 | 22 | 2.5 | 380 | 303 | 33 | 34 | 37.29 | 14 | 33 | 34 | 37.29 | 24 |
| M24 | 24 | 3 | 452 | 353 | 35 | 36 | 39.55 | 15 | 35 | 36 | 39.55 | 26 |
| M27 | 27 | 3 | 573 | 459 | 40 | 41 | 45.2 | 17 | 40 | 41 | 45.2 | 30 |
| M30 | 30 | 3.5 | 707 | 561 | 45 | 46 | 50.85 | 18.7 | 45 | 46 | 50.85 | 33 |
| M36 | 36 | 4 | 1020 | 817 | 53.8 | 55 | 60.79 | 22.5 | 53.8 | 55 | 60.79 | 39 |
Socket Head Countersunk Black Bolts
Bolt dimensions and area for countersunk bolts black bolts (non-preloaded) with a hex socket head (as opposed to slot head) in accordance with BS EN ISO 10642 are given in the table below. Countersunk bolts can be attached into a pre-tapped hole or via a nut as with a standard hex head bolt. Note, countersunk bolts should only be used for functional reasons, such as on a sliding or bearing surface, countersunk bolts should not be used for aesthetic reasons. In addition, it is worth noting that another British Standard for countersunk bolts exists, BS 4933:2010.
| Bolt dimensions | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Reference | Nominal Diameter (mm) | Pitch (mm) | Unthreaded Area (mm²) | Stress Area (mm²) | Head Diameter Min (mm) | Head Diameter Max (mm) | Min Diameter of Unthreaded Shank (mm) | Max Diameter of Unthreaded Shank (mm) | Head Thickness max (mm) | Hex Socket Across Flats Min (mm) | Hex Socket Across Flats Max (mm) | Hex Socket Across Corner to Corner (mm) | Hex Socket Depth (mm) | Hole Diameter (mm) |
| M6 | 6 | 1 | 28.3 | 36.6 | 11.34 | 13.44 | 5.82 | 6 | 3.72 | 4.095 | 4.02 | 4.58 | 2.2 | 7 |
| M8 | 8 | 1.25 | 50.3 | 58 | 15.24 | 17.92 | 7.78 | 8 | 4.96 | 5.14 | 5.02 | 5.72 | 3 | 9 |
| M10 | 10 | 1.5 | 78.5 | 84.3 | 19.22 | 22.4 | 9.78 | 10 | 6.2 | 6.14 | 6.02 | 6.86 | 3.6 | 11 |
| M12 | 12 | 1.75 | 113 | 157 | 23.12 | 26.88 | 11.73 | 12 | 7.44 | 8.175 | 8.025 | 9.149 | 4.3 | 13 |
| M16 | 16 | 2 | 201 | 245 | 29.01 | 33.6 | 15.73 | 16 | 8.8 | 10.175 | 10.025 | 11.43 | 4.8 | 18 |
| M20 | 20 | 2.5 | 314 | 245 | 36.05 | 40.32 | 19.67 | 20 | 10.16 | 12.212 | 12.032 | 13.72 | 5.6 | 22 |
Preloaded (HSFG) Bolts
Bolt dimensions for preloaded bolts (HSFG) in accrodance with BS EN 14399-3 (HR Bolts), BS EN 14399-10 (HRC Bolts) and BS EN 14399-3 (Nuts) are given in the table below:
| Bolt dimensions | Nut dimensions | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Reference | Nominal Diameter (mm) | Pitch (mm) | Unthreaded Area (mm²) | Stress Area (mm²) | Width Across Flats - min (mm) | Width Across Flats - max (mm) | Width Across Corners - max (mm) | Head Thickness Min (mm) | Head Thickness Max (mm) | Width Across Flats - min (mm) | Width Across Flats - max (mm) | Width Across Corners - max (mm) | Hole Diameter (mm) | ||
| M12 | 12 | 1.75 | 113 | 84.3 | 21.16 | 22 | 23.91 | 7.05 | 7.95 | 21.16 | 22 | 23.91 | 13 | ||
| M16 | 16 | 2 | 201 | 157 | 26.16 | 27 | 29.56 | 9.25 | 10.75 | 26.16 | 27 | 29.56 | 18 | ||
| M20 | 20 | 2.5 | 314 | 245 | 31 | 32 | 35.03 | 11.6 | 13.4 | 31 | 32 | 35.03 | 22 | ||
| M22 | 22 | 2.5 | 380 | 303 | 35 | 36 | 39.55 | 13.1 | 14.9 | 35 | 36 | 39.55 | 24 | ||
| M24 | 24 | 3 | 452 | 353 | 40 | 41 | 45.2 | 14.1 | 15.9 | 40 | 41 | 45.2 | 26 | ||
| M27 | 27 | 3 | 573 | 459 | 45 | 46 | 50.85 | 16.1 | 17.9 | 45 | 46 | 50.85 | 30 | ||
| M30 | 30 | 3.5 | 707 | 561 | 49 | 50 | 55.37 | 17.65 | 19.75 | 49 | 50 | 55.37 | 33 | ||
| M36 | 36 | 4 | 1020 | 817 | 58.8 | 60 | 66.44 | 21.45 | 23.55 | 58.8 | 60 | 66.44 | 39 | ||
Preloaded (HSFG) Countersunk Bolts
Bolt dimensions for countersunk preloaded bolts (HSFG) in accrodance with BS EN 14399-7 are given in the table below. Countersunk preloaded bolts are driven by a recessed slot socket in the head, instead of a hex socket head. Countersunk bolts can be attached into a pre-tapped hole or via a nut as with a standard preloaded bolt. Note, countersunk bolts should only be used for functional reasons, such as on a sliding or bearing surface, countersunk bolts should not be used for aesthetic reasons.
| Bolt dimensions | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Reference | Nominal Diameter (mm) | Pitch (mm) | Unthreaded Area (mm²) | Stress Area (mm²) | Head Diameter Min (mm) | Head Diameter Max (mm) | Min Diameter of Unthreaded Shank (mm) | Max Diameter of Unthreaded Shank (mm) | Head Thickness nom (mm) | Slot Length Min (mm) | Slot Length Max (mm) | Slot Depth Min (mm) | Slot Depth Max (mm) | Slot Width Min(mm) | Slot Width Max (mm) | Hole Diameter (mm) |
| M12 | 12 | 1.75 | 113 | 84.3 | 23.16 | 24 | 11.3 | 12.7 | 8 | 15.5 | 16.5 | 3 | 4.5 | 2.5 | 3 | 13 |
| M16 | 16 | 2 | 201 | 157 | 31.16 | 32 | 15.3 | 16.7 | 10 | 21.5 | 22.5 | 3 | 4.5 | 2.5 | 3 | 18 |
| M20 | 20 | 2.5 | 314 | 245 | 39 | 40 | 19.16 | 20.84 | 13 | 27.5 | 28.5 | 3.5 | 5 | 3 | 3.5 | 22 |
| M22 | 22 | 2.5 | 380 | 303 | 43 | 44 | 21.16 | 22.84 | 14 | 29.5 | 30.5 | 3.5 | 5 | 3 | 3.5 | 24 |
| M24 | 24 | 3 | 452 | 353 | 47 | 48 | 23.16 | 24.84 | 16 | 32.5 | 33.5 | 3.5 | 5 | 3 | 3.5 | 26 |
| M27 | 27 | 3 | 573 | 459 | 53 | 54 | 26.16 | 27.84 | 17.5 | 36.5 | 37.5 | 3.5 | 5 | 3 | 3.5 | 30 |
| M30 | 30 | 3.5 | 707 | 561 | 58.8 | 60 | 29.16 | 30.84 | 19.5 | 41.5 | 42.5 | 4 | 5.5 | 3.5 | 4 | 33 |
| M36 | 36 | 4 | 1020 | 817 | 70.8 | 72 | 35 | 37 | 23 | 49.5 | 50.5 | 4 | 5.5 | 3.5 | 4 | 39 |
From the above tables it is clear to see that preloaded bolts are chunkier than the equivilant black bolt, this is due to the need for preloaded bolts to withstand additional preloading force to clamp mating surfaces together. The differenc between HR and HRC is briefly:
- HR bolts - Stands for High Resistance bolts. These bolts are designed to fail through yield of the bolt threads within the main shank, as opposed to the HV system that relies on the yield of the threads within the nut. Only HR bolts are used in the UK as they are less susceptible to over-tightening and any bolt failures are readily detectable as the bolt fails and will either fall out of the hole or be noticably loose.
- HRC bolts - Stands for High Resistance Calibrated, these bolts are manufactured for easy installation, controlling the tension of the install bolt through a physical indicator, such as an element shearing at a defined load. A widely used example of a HRC bolts are TCBs (Tension Control Bolts), these control the preload in the bolt through the shearing off of a special installation bolt tip at a given torque.
- From a design point of view, HR and HRC bolts can be used interchangeably. However, the contractor constructing the design may have a preference.
It should be noted that some weathering steel preloaded bolts are available. However, there is only a very limited range of sizes in weathering steel, the designer should satisfy themselves that the bolt size is available prior to commencing the detailed design.
An video showing how TCBs are installed is embedded below, this has been shared from the TCB website located here