Non-preloaded Structural Bolt Assembly BS EN 15048 (CE & UKCA Certified)
Equivalent Standard: ISO 7412
EN 15048 is a European standard that specifies the requirements for non-preloaded structural bolting assemblies, including bolts, nuts, and washers. This assembly is used in general steel construction where preloading (controlled tensioning) is not required. Unlike high-strength preloaded bolts (e.g., EN 14399 for HV bolts), these assemblies are not tensioned to a specified preload and rely on bearing-type connections rather than friction-grip connections.
BS EN 15048 is the European standard for non-preloaded structural bolts offers a simple, cost-effective solution for non-critical connections in European construction. Unlike A490 or EN 14399 bolts, these are simpler to install and do not require controlled preloading, making them suitable for less critical connections. However, for high-strength, slip-resistant joints, EN 14399-1 or ASTM A325/A490 should be used instead.
Application & Use
- Common in secondary steel structures, bracing, and non-load-bearing connections.
- Not suitable for dynamic or fatigue-prone applications(e.g., bridges, cranes), where preloaded bolts (EN 14399) are preferred.
- Applies to bolted connections in structural engineering(buildings, towers, non-critical steel frames).
- Suitable for bearing-type connections(load transfer through bolt shear/bearing, not friction).
- Used in non-critical, static structures where slip resistance is not required. For high-fatigue applications (, use EN 14399 preloaded bolts).
EN 15048
BS EN 15048 is a European standard series for non-preloaded structural bolting assemblies these are simpler to install and do not require controlled preloading, making them suitable for less critical connections.
Components & Grades
- Bolts: Typically property class 4.6, 5.6, 6.8, or 8.8 (similar to ISO 898-1).
- Nuts: Must match or exceed bolt strength (e.g., class 5 for 5.6 bolts, class 8 for 8.8 bolts).
- Washers: Usually flat, unhardened washers.
Coating & Corrosion Protection
Unlike high-strength bolts (EN 14399 or ASTM A490), EN 15048 bolts can be coated with::
- Hot-dip galvanized (HDG)
- Electroplated (e.g., zinc-plated)
- Dacromet-coated(if corrosion resistance is needed without hydrogen risk)
- Hydrogen embrittlement riskmust be managed for 8 and higher grades if electroplated.
Assembly & Installation
- No preloading (torquing to a specific tension) required.
- Tightened to “snug-tight” condition(firm contact, but no measured preload).
- No requirement for load-indicating washers or torque control methods(unlike EN 14399).
Technical Specification for Non Preloaded Structural Bolt Assemblies (EN 15048)
| BS EN 15048 Fully Threaded Bolt Dimensions. Classes 8.8 & 10.9 | |||||||
| Nom. Dia. (d) | M12 | M16 | M20 | M24 | M30 | M36 | |
| Thread Pitch | 1.75 | 2.00 | 2.50 | 3.00 | 3.50 | 4.00 | |
| a | Max. | 5.25 | 6.00 | 7.50 | 9.00 | 10.50 | 12.00 |
| s | Min. | 17.57 | 23.16 | 29.16 | 35.00 | 45.00 | 53.80 |
| Max. | 18.00 | 24.00 | 30.00 | 36.00 | 46.00 | 55.00 | |
| e | Min. | 19.85 | 26.17 | 32.95 | 39.55 | 50.85 | 60.79 |
| df | Min. | 16.47 | 22.00 | 27.70 | 33.25 | 42.75 | 51.11 |
| c | Min. | 0.15 | 0.20 | 0.20 | 0.20 | 0.20 | 0.20 |
| Max. | 0.60 | 0.80 | 0.80 | 0.80 | 0.80 | 0.80 | |
| r | Min. | 0.60 | 0.60 | 0.80 | 0.80 | 1.00 | 1.00 |
| de | Max. | 13.70 | 17.70 | 22.40 | 26.40 | 33.40 | 39.40 |
| k | Min. | 7.32 | 9.71 | 12.15 | 14.65 | 18.28 | 22.08 |
| Max. | 7.68 | 10.29 | 12.85 | 15.35 | 19.12 | 22.92 | |
Mechanical Properties of EN 15048
Property Class | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) |
4.6 | 400 | 240 | 20 |
5.6 | 500 | 300 | 18 |
6.8 | 600 | 480 | 12 |
8.8 | 800 | 640 | 12 |
EN 15048 Comparison with Other Standards
Feature | BS EN 15048 (Non-Preloaded) | EN 14399 (Preloaded HV) | ASTM A325/A490 (Preloaded) |
Preload Required? | No | Yes | Yes |
Strength Grades | 4.6 to 8.8 | 8.8 & 10.9 | A325 (≈8.8), A490 (≈10.9) |
Coating Allowed? | Yes (HDG, plating, etc.) | Limited (hydrogen risk) | A490: No HDG/plating (except Dacromet) |
Typical Use | Secondary structures | Critical connections | Heavy steel construction |
| Bolt Thread Diameter | Tensile Strength | Proof Load | Elongation | Hardness Rockwell HRC | |
| N/mm2 min. | N/mm2 min. | % Min. | Min. | Max. | |
| M12 | 800 | 660 | 12 | 23 | 34 |
| M16 | 830 | 660 | 12 | 23 | 34 |
| M20 | 830 | 660 | 12 | 23 | 34 |
| M22 | 830 | 660 | 12 | 23 | 34 |
| M24 | 830 | 660 | 12 | 23 | 34 |
| M27 | 830 | 660 | 12 | 23 | 34 |
| M30 | 830 | 660 | 12 | 23 | 34 |
| M36 | 830 | 660 | 12 | 23 | 34 |
| EN 15048 Assemblies also require a Charpy Impact Test to EN 10045-1 | |||||
BS EN 15048 Nut Dimensions
| Nominal size and thread diameter d | Pitch of thread p | Width across flats s | Width across corners e | Thickness of nut m | ||
| Max. | Min. | Min. | Max. | Min. | ||
| M12 | 1.75 | 18.00 | 17.57 | 21.10 | 10.80 | 10.37 |
| M16 | 2.00 | 24.00 | 23.67 | 26.75 | 14.80 | 14.10 |
| M20 | 2.50 | 30.00 | 29.16 | 32.95 | 18.00 | 16.90 |
| M24 | 3.00 | 36.00 | 35.00 | 39.55 | 21.50 | 20.20 |
| M30 | 3.50 | 46.00 | 45.00 | 50.85 | 25.60 | 24.30 |
| M36 | 4.00 | 55.00 | 53.80 | 60.79 | 31.00 | 29.40 |
When to Use BS EN 15048 Bolts?
✔ Non-slip-critical connections (e.g., bracing, light frames).
✔ Cost-effective solution (no need for special tightening procedures).
✔ Where dynamic/fatigue loads are not a concern.
When to Avoid?
✖ Slip-critical or seismic applications (use EN 14399 or A325/A490 instead).
✖ High-vibration environments (risk of loosening).