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Connecting elements for structural wood and steel construction

DIN EN 1090 describes the design of steel structures and aluminum structures, and Part 2 contains the technical rules for the design of steel structures. There, the use of high-strength bolts for steel construction is prescribed and the corresponding standards are also specified for this.

HV fittings for screw connections

HV is the designation of a bolted joint in steel construction with high-strength pretensionable bolts of strength class 10.9. H stands for high-strength (material property) and V stands for pretensioned (condition of the bolt). According to DIN EN 14399-4, HV sets are hexagonal bolts and -nuts that are standardized in the range M 12 to M 36. The associated washers are standardized in DIN EN 14399-6.

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In summary, as an area of application, steel structures such as, among others, hall, bridge and industrial buildings, cableway installations and masts, high-voltage pylons and wind turbines.  

The HV bolts are used in shear connections (shear-hole-bonded connections, slip-resistant connection in the serviceability limit state and slip-resistant connection in the ultimate limit state) and in tension connections (non-prestressed and prestressed).

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What steel construction customers particularly appreciate about us

  • Highest quality, because we do not compromise with our products. Tightening torques are responsible for the preload force, but this can only be maintained if the friction values are also determined correctly. Due to our high quality standards and our experience as one of the A suppliers in the automotive sector, we have the corresponding knowledge and equipment.

  • Everything from a single source in brand quality: We provide you with a comprehensive steel construction product portfolio that is sure to leave nothing to be desired. This does not end with fasteners - tools and industrial safety materials round off our product range.

  • Our steel construction team is ready for you: With your dedicated contact person, we always have your requirements in mind - supported by our own quality assurance department with 40 employees and an engineering and application technology department with 10 employees.

  • Piece-precise construction site delivery - whether piece-precise delivery or deviating delivery address - we make both possible.

Quality criteria

HV bolts are safety-relevant and must meet strict quality criteria. The specified ratio of tightening torque to preload force ensures a high level of application safety. Strength class 10.9 bolts (with large width across flats) allow better utilization of bolt strength compared with normal steel bolts. Fewer bolts are required for the same frictional connection, or smaller HV bolts can be used, resulting in cost savings for all connections.


There are two methods for achieving the defined preload force.

  • The modified torque method (EN 1993-1-8), in which a defined torque is applied step by step by means of a torque wrench and thus the reduced preload force can be achieved.

  • The combined pretensioning method (EN 1090-2), in which a defined pretensioning torque is first applied and then the nut is tightened at a defined further rotation angle. With this method, the full preload force is achieved.

The specified torques and angles can be taken from the assembly instructions, or from our practical HV calculation slider.

Important facts

  • only complete sets (bolt, nut and washers) from one manufacturer may be used

  • Ii a prestressed clothing is loosened, it must be replaced by a new one

  • all screw sets must bear the CE mark (to be affixed to labels)

  • the manufacturer of the HV bolted joints shall keep a copy of the certificate of conformity to the relevant standards, provide and confirm that the factory production control has been approved by a third party audit

  • Documents confirming the quality of the set should be kept by the manufacturer and delivered at the request of the recipient within two working days

  • HV bolts, nuts and washers must be protected from corrosion and contamination during storage

  • HV screws are given a unique identification number and a guide number to ensure full traceability and easy access to detailed test results


The Lindapter product portfolio offers high-strength connections that can be made quickly by clamping two steel profiles together - without drilling and welding. Lindapter offers you a selection guide on the web so that you can always find the right solution for your specific application.

Selection guide

Fastening assortment

In order to connect steel structures to the existing building, you need connections that are approved for the various applications. Keller & Kalmbach offers you the right product for every application with the Fischer, Upat and FAKKT brands.

Tool & Equipment

In addition to design, assembly plays a major role. Without the right equipment, a smooth process cannot be guaranteed. Complementing the connection solutions, Keller & Kalmbach offers the right tools and equipment for every application.

FAKKT wood construction screws

FAKKT timber construction screws are used in solid wood, timber frame and structural timber construction. They are suitable for connections of two or more structural members, especially in applications where structural verification is required.

Our dimensioning program for roof systems, specially tailored to FAKKT screws, can be used to quickly and easily calculate and verify the optimum use of the required screws for the specific application. Thanks to the ETA approval, the screw is also approved for safety-relevant applications.

Advantages of the FAKKT screw

  • High bending moment of the screw up to 105°, thus high safety, the screw can move along in the wood under different weather conditions
  • Innovative head of the plate head variant ensures flush termination in the wood, support of a counter-battening is possible without any problems
  • Can be used regardless of season, the high bending angle ensures that the screw can also be screwed in during extreme temperature fluctuations
  • Optimized processing speed, because the tip of the FAKKT wood construction screw is self-tapping, which eliminates the need for pre-drilling
  • Easy installation, thanks to the shaft ribs, which reduce the torque when screwing in and create a chip-free connection