UNI 5712 High Strength Structural Bolts
UNI 5712 high strength structural bolts are designed for bolted steel connections where a robust head configuration and high-strength fastening are required. The large hexagon head provides a wide bearing area and positive engagement with standard tightening tools, making the bolts suitable for structural assemblies where reliable tightening and load transfer are important.
The bolt design incorporates an ISO metric coarse thread and a large width across flats in proportion to the bolt diameter. This configuration provides practical advantages during installation and tightening, particularly for steel fabrication and heavy-duty structural connections. UNI 5712 bolts can be supplied in different nominal diameters, lengths, material grades, and surface finishes according to the required specification. We can also manufacture or supply bolts based on customer drawings and existing UNI 5712 requirements, with dimensional and mechanical inspection available for production orders.
Specification:
UNI 5712 is the former Italian dimensional reference for large-hexagon bolts used in structural steelwork. The product is associated with the European high-strength structural bolting system now specified by EN 14399-4. The current EN 14399-4 standard covers HV system bolt and nut assemblies for preloaded structural joints, with large widths across flats, thread sizes from M12 to M36, and property class 10.9/10.
The bolt dimensions include the large hexagon head, nominal diameter, head height, width across flats, thread length, and grip length. The metric thread system is based on ISO metric coarse threads, with ISO 261 defining the general plan for diameter and pitch combinations and ISO 965-2 providing the applicable limits of sizes and tolerance system for general-purpose metric threads. For structural preloaded applications, UNI 5712-type bolts are normally used together with the corresponding structural nuts and washers as a matched assembly. Under the current EN 14399 system, EN 14399-1 defines general requirements, EN 14399-2 covers suitability for preloading, and EN 14399-4 specifies the HV hexagon bolt and nut assembly. Washers are specified according to EN 14399-6.
| Parameter | Specification |
|---|---|
| Standard | UNI5712/EN14399-4 |
| Structural System | HV |
| Application | Preload Structural Joint |
| Size Range | M12-M36 |
| Property Class | 10.9 |
| Thread | Metric Coarse |
| Thread Standard | ISO261/ISO965 |
| Head Type | Large Hexagon Head |
| Nut | EN14399-4 Compatible Structural Nut |
| Washer | EN14399-6 |
| Preloading Requirement | EN14399-2 |
Dimension Chart of UNI5712 Italy Standard Large Structural Bolt:
| Thread Diameter | M12 | M14 | M16 | M18 | M20 | M22 | M24 | M27 |
| P | 1.75 | 2 | 2 | 2.5 | 2.5 | 2.5 | 3 | 3 |
| b max | 23 | 25 | 28 | 30 | 33 | 34 | 37 | 39 |
| b min | 21 | 23 | 26 | 28 | 31 | 32 | 34 | 37 |
| s max | 22 | 24 | 27 | 30 | 32 | 36 | 41 | 46 |
| s min | 21.16 | 23.16 | 26.16 | 29.16 | 31 | 35 | 40 | 45 |
| da max | 15.2 | 17.2 | 19.2 | 21.2 | 24 | 26 | 28 | 32 |
| ds max | 12.7 | 14.7 | 16.7 | 18.7 | 20.84 | 22.84 | 24.84 | 27.84 |
| ds min | 11.3 | 13.3 | 15.3 | 17.3 | 19.16 | 21.16 | 23.16 | 26.16 |
| e min | 23.91 | 27.34 | 29.56 | 34.27 | 35.03 | 39.55 | 45.2 | 50.85 |
| k max | 8.45 | 9.75 | 10.75 | 12.9 | 13.9 | 14.9 | 15.9 | 17.9 |
| k min | 7.55 | 8.25 | 9.25 | 11.1 | 12.1 | 13.1 | 14.1 | 16.1 |
| r min | 1.2 | 1.2 | 1.2 | 1.2 | 1.5 | 1.5 | 2 | 2 |
Application of UNI5712 Large Structural Bolts:
UNI 5712 high strength structural bolts are used for steel columns, beams, trusses, frames, and other fabricated steel structures where bolted joints are required to transfer loads between structural members. Their large hexagon head is suited to structural connections requiring controlled tightening and robust mechanical fastening.
Bridges & Infrastructure
These large-hexagon structural bolts are suitable for bridge steelwork, highway structures, railway infrastructure, towers, and other heavy steel construction projects. They can be used in connections where high-strength structural bolting assemblies are specified for load-bearing joints.
Industrial Steel Structures
UNI 5712 bolts can also be used in industrial buildings, steel platforms, equipment supports, warehouses, cranes, and fabricated structural frames. The bolts can be supplied with compatible nuts and washers for complete structural fastening assemblies.
Preloaded Structural Connections
For structural joints requiring preloading, UNI 5712-type bolts can be specified as part of a matched high-strength structural bolting assembly. Under the current European system, EN 14399 covers preloaded structural bolting assemblies, including the HV bolt and nut system specified by EN 14399-4.