EN 14399 High-Strength Structural Bolting: HV and HR Systems Explained

EN 14399 Series: Europe's Structural Bolting Standard

EN 14399 is a ten-part European standard covering high-strength structural bolting assemblies for preloading used in steel construction. Unlike pressure equipment fasteners (governed by PED), structural bolts are designed for tension and shear loads in building frames, bridges, towers, and industrial structures. EN 14399 superseded older DIN and ISO structural bolting standards across the EU and is mandatory for CE-marked structural steel construction.

System Types: HV vs HR

EN 14399 defines two primary bolting systems:

• HV System (EN 14399-3 and -4): High-strength hexagon bolt and nut assemblies with a large washer under the nut. The bolt threads engage through both connected members and the nut. Washer spreads the preload and prevents nut embedment into the steel surface. This is the most common system for structural steel connections.
• HR System (EN 14399-3 and -6): High-strength bolt and nut assemblies designed for structural connections with specific preload requirements. HR assemblies include specially designed bolts with waisted shanks or specific thread runout characteristics.

System Comparison Table

Feature	HV System	HR System
Bolt Type	Hex head bolt	High-strength bolt sets
Washer Requirement	Large washer under nut (mandatory)	Per assembly design
Typical Grades	8.8, 10.9	8.8, 10.9
Thread Form	ISO metric coarse	ISO metric coarse
Preload Method	Torque, combined, DTI	Torque, combined, DTI
Primary Application	Steel frame connections	Slip-critical connections

Strength Grades: 8.8 and 10.9

EN 14399 structural bolts are manufactured to property class 8.8 or 10.9 per ISO 898-1. Class 8.8 provides 800 MPa nominal tensile strength; Class 10.9 provides 1000 MPa. The choice depends on the structural engineer's load calculation and connection design. Class 10.9 is preferred for slip-critical connections where joint slip under working load must be prevented.

Preloading Methods per EN 1090-2

EN 1090-2 (execution standard for structural steelwork) recognizes three preloading methods:

• Torque Method: Apply specified torque using calibrated torque wrench. Friction coefficient K must be specified (typically K=0.12-0.16 for as-delivered finish).
• Combined Method: Impact wrench with calibrated pneumatic or hydraulic tool, followed by verification of nut rotation angle from snug-tight condition.
• Direct Tension Indicator (DTI): Specialized washer with raised bumps that compress at specified preload. Visual inspection confirms proper preload when gap closes.

CE Marking and Declaration of Performance

EN 14399 fasteners for structural steel construction must bear CE marking and be accompanied by a Declaration of Performance (DoP) per the Construction Products Regulation (CPR) 305/2011. The manufacturer must hold factory production control (FPC) certification from a notified body. LOKRON holds CE marking authorization for EN 14399-3 and -4 HV system components under CPR.

Differences from ASTM A325/A490

Feature	EN 14399	ASTM A325/A490
Thread Form	ISO metric	Unified (UNC)
Strength Classes	8.8, 10.9	A325 (120 ksi), A490 (150 ksi)
Marking	Manufacturer ID + grade	A325 or A490 marking
Washer Requirement	Mandatory large washer (HV)	Hardened washer under turned element
Primary Market	Europe, Middle East	North America

LOKRON's EN 14399 Capability

LOKRON manufactures EN 14399-3 and -4 HV system bolts, nuts, and washers in sizes M12 through M36, property classes 8.8 and 10.9, with full CE marking and DoP. Our products are used in structural steel projects across the UK, Germany, Poland, and UAE.