Strut Bolt
Structural blind bolt for hollow steel profiles – the improved "Boxbolt".
Technical Specification
| Characteristics | Steel blind bolt for connecting to a hollow profile – the "BOXBOLT" type. |
| Material | Carbon steel, grade 8.8 (ISO 898-1) |
| Coating | SBZ – zinc plated 5–8 µm (ISO 4042) | SBG – hot-dip galvanized 40–50 µm (EN ISO 10684) |
| Technology | Expanding structural blind bolt |
| Sizes | M6, M8, M10, M12, M16, M20 |
| Compatible profiles | Square (SHS), rectangular (RHS) and circular (CHS) |
| Fire class | A1 according to EN 13501-1 |
| Approval | European Technical Assessment ETA 25/0373 (April 2025) |
Files to Download
- Strutbolt anchor, the improved "Boxbolt" – technical data
- Strutbolt – European Technical Assessment (ETA)
- Strutbolt – Certificate of Constancy of Performance (CoCP)
- Strutbolt – Declaration of Performance (DoP)
Installation Video
What is the Strut Bolt and How Does It Work?
Connecting to a hollow profile – square (SHS), rectangular (RHS) or circular (CHS) – presents the same problem to every engineer and installer: there is no access to the far side of the profile to fit a conventional nut. Welding is possible but expensive and cumbersome, it needs surface finishing, and it is not always feasible on site. Ordinary bolts simply do not work.
That is why blind bolt technology exists, and the Adit Strut Bolt is its most advanced expression. It is a structural anchor for hollow profiles, manufactured by INDEX and distributed exclusively in Israel by Adit Ltd. It holds European Technical Assessment ETA 25/0373 (April 2025).
How it works: drill a hole of the right diameter, insert the anchor from one side only, and tighten – first with an impact driver for the initial lock, then with a torque wrench for the final tightening. The tail of the anchor expands behind the inner wall of the profile and creates a solid, rigid and safe grip, with no need for access to the far side and no welding.
Key Technical Characteristics
Technology
Expanding structural blind bolt.
Raw material
Carbon steel, strength grade 8.8 (ISO 898-1) – the leading standard for construction.
Available finishes
Zinc plated (SBZ, 5–8 µm) or hot-dip galvanized (SBG, 40–50 µm) for high corrosion resistance.
Available sizes
From M6 up to M20, carrying very substantial loads.
Compatibility
Suitable for square, rectangular and circular profiles.
Fire standard
Fire resistance class A1 according to EN 13501-1.
Why the ETA Matters
The European Technical Assessment is the strictest and most comprehensive approval for structural anchors in the world. It is issued by a recognised assessment body after a series of in-depth destructive tests – tension, shear, performance under extreme conditions and more.
The Strut Bolt holds ETA 25/0373 in accordance with EAD 330001-00-0602, written specifically for expanding assemblies used in blind connections. For the engineer and the contractor that means:
- The nominal force values (tension and shear) are approved and audited by an independent European body.
- The anchor is explicitly intended for structural connections – not only for light applications.
- The values can be used for official structural design according to Eurocode 3 (EN 1993).
- AVCP system 2+ ensures continuous production surveillance.
Worth knowing: many competing hollow profile anchors on the Israeli market do not hold a valid ETA. Choosing the Strut Bolt means using an approved product with professional backing, legal accountability and full compliance with European standards.
Approved Load Values
Characteristic failure loads and approved design loads according to ETA 25/0373. These are the values officially approved for use in structural design.
| Anchor size | Tension Nrk [kN] | Shear Vrk [kN] | Design tension Nrd [kN] | Design shear Vrd [kN] |
|---|---|---|---|---|
| M6 | 16.1 | 20.4 | 12.9 | 16.3 |
| M8 | 28.9 | 36.4 | 23.1 | 29.1 |
| M10 | 44.7 | 59.2 | 35.8 | 47.4 |
| M12 | 51.4 | 80.3 | 41.1 | 64.2 |
| M16 | 101.5 | 145.6 | 81.2 | 116.5 |
| M20 | 132.7 | 229.1 | 106.2 | 183.3 |
Source: ETA 25/0373, Annex C2. These values are approved for design according to Eurocode 3.
Strut Bolt vs. Boxbolt BQ_S
For years the British Boxbolt was the benchmark in this field. The comparison below is based on the official performance data of both products – the Adit Strut Bolt against the equivalent Boxbolt BQ_S anchor.
| Size | Boxbolt shear [kN] | Strut Bolt shear [kN] | Advantage | Boxbolt tension [kN] | Strut Bolt tension [kN] | Advantage |
|---|---|---|---|---|---|---|
| M6 | 17.6 | 20.4 | +15.9% | 12.7 | 16.1 | +26.8% |
| M8 | 31.6 | 36.4 | +15.2% | 23.1 | 28.9 | +25.1% |
| M10 | 57.1 | 59.2 | +3.7% | 36.5 | 44.7 | +22.5% |
| M12 | 72.4 | 80.3 | +10.9% | 53.1 | 51.4 | Comparable |
| M16 | 131.6 | 145.6 | +10.6% | 98.9 | 101.5 | +2.6% |
Conclusion: in 4 of 5 sizes the Strut Bolt is significantly stronger than the Boxbolt in shear, and in almost every size it is stronger in tension.
Hot-Dip or Zinc Plated? Choosing the Right Protection
SBZ – Zinc Plated
Zinc coating of 5–8 microns (ISO 4042). Suitable for indoor environments – warehouses, industrial buildings, covered bridges. Excellent durability of over 50 years in a C1 indoor corrosion environment.
SBG – Hot-Dip Galvanized
Massive zinc coating of 40–50 microns (EN ISO 10684). Intended for outdoor environments, coastal areas and heavy industry. Over 50 years of durability in a C2 environment, and up to 47 years in a demanding C3 environment.
Six Reasons to Choose the Strut Bolt
Approved performance (ETA)
Every load value is officially approved by an independent European body – no invented figures and no "manufacturer estimates".
Blind fastening
No access needed to the far side of the profile, no welding, and no second person holding a nut.
Fits every hollow profile
Square (SHS), rectangular (RHS) and circular (CHS), across all common wall thicknesses.
The widest size range
From M6 for light connections such as signage, up to a formidable M20 carrying 229 kN in shear for primary structural work.
Major cost savings
Welding needs a certified welder, paint finishing, non-destructive testing and cooling time. The Strut Bolt needs a drilled hole and a driver – saving expensive labour hours.
Durability and service life
Strong 8.8 steel combined with the hot-dip galvanized option gives an engineering solution good for half a century.
Photo Gallery
Frequently Asked Questions
What is a hollow profile anchor, and how is it different from an ordinary bolt or a concrete anchor?
An ordinary steel bolt needs access to both sides in order to thread and tighten a nut. In a hollow steel profile (SHS/RHS/CHS) – a closed steel column or a rectangular beam – there is no access to the inside of the profile at all.
A hollow profile anchor (blind bolt) is designed to be inserted from one side only. As it is tightened, its steel mechanism expands behind the inner wall and locks the connection under force.
Why is connecting to an RHS/SHS profile considered a complex engineering challenge?
Because simple bolts and nuts cannot be used. For years the common solution was structural welding – a process that requires a certified welder on site, damages the original galvanized layer of the steel, can weaken the profile through heat, and demands expensive non-destructive testing afterwards. Anchors like the Strut Bolt bypass all of this with cold drilling and mechanical tightening.
What is the difference between the Strut Bolt and a Lockbolt?
Both are advanced fastening solutions, but they work differently. A Lockbolt is usually made of a pin and a collar, requires access to both sides or is used as a rivet for thin sheet, and works by pulling and swaging with a special dedicated tool. The Strut Bolt is a true blind bolt intended for substantial structural wall thicknesses, installed from one side only, and needs nothing more than standard tools – a driver and a torque wrench.
Which anchor sizes are suitable for hollow profiles?
The Strut Bolt series is available in M6, M8, M10, M12, M16 and M20. The choice depends on the calculated loads and the wall thickness of the profile. Every size (and every length within the same size) has a permitted fixture thickness range (tfix). Verify the technical data with the Adit engineering team before ordering.
Can a hollow profile anchor be used for primary structural connections (heavy construction)?
Yes, absolutely – as long as the anchor holds an approved European Technical Assessment, as the Strut Bolt does (BWR1, mechanical resistance and stability). It can then be used with confidence in primary structural connections, with the loads designed according to Eurocode 3. Design always remains the responsibility of the structural engineer.
Can a chemical anchor be used instead of a steel anchor in a hollow profile?
No. A chemical anchor is designed for anchoring into cementitious materials, stone or concrete, where the resin fills the drilled hole and bonds to its walls. In a connection to a hollow steel profile there is neither enough surface area for the resin to bond to, nor any base material for it to hold onto. A steel-to-steel connection in a closed cavity requires a mechanical anchor.
How much load can an M16 Strut Bolt really carry?
The M16 Strut Bolt carries a characteristic failure load of 101.5 kN in tension and 145.6 kN in shear – over 14 tons. The design loads (after the engineering safety factor of 1.25) are 81.2 kN in tension and 116.5 kN in shear. Those figures make it an excellent alternative to welding on heavy profiles.
Do the Boxbolt and the Strut Bolt work on the same principle? Which is better?
Yes – both are expanding blind bolts installed from one side of the profile and tightened to a torque. The Boxbolt was for years the industry default, but today the INDEX Strut Bolt delivers higher shear and tension figures, carries a more advanced and more recent ETA (April 2025), and is offered at a competitive price with full availability in Israel through Adit.
Can the Strut Bolt be used in a round profile (a steel tube)?
Yes. The Strut Bolt is suitable for square, rectangular and circular profiles alike. The one thing to check in a circular profile is that the internal cavity is wide enough for the anchor to open and expand fully according to the specification.
Does installing a Strut Bolt need a special tool? What torque is required?
No. Unlike methods such as the Lockbolt, which need an expensive dedicated hydraulic pulling tool, the Strut Bolt is installed with an ordinary impact driver for the initial lock and a standard torque wrench for the final tightening.
Installation torques (Tinst): M6 = 13 Nm | M8 = 23 Nm | M10 = 45 Nm | M12 = 80 Nm | M16 = 190 Nm | M20 = 300 Nm. Do not tighten beyond the specified torque.
Can a Strut Bolt be removed and re-installed?
No. The blind bolt works by irreversible mechanical deformation and expansion inside the hollow profile. Once it has been installed and tightened to the required torque, it becomes a permanent connection. The central bolt can be removed in order to release the outer element, but the inner anchoring sleeve stays locked inside the beam.
Is the Strut Bolt suitable for dynamic loads and vibration?
According to ETA 25/0373 the anchor is approved for design under static and quasi-static loads. For applications involving sustained fatigue loading – such as lifting installations or heavily vibrating machinery – consult a structural engineer and the Adit engineering team in advance to verify applicability and safety.