Strut Bolt

Structural blind bolt for hollow steel sections – the improved "Boxbolt". Single-sided installation, no welding, European ETA approval.

ETA 25/0373M6 – M20Steel grade 8.8SBZ / SBG galvanizingFire class A1

Technical specification

Property	Strut Bolt — structural blind bolt, European approval
Characteristics	Steel expansion anchor for connection to "BOXBOLT"-type hollow sections
Raw material	Carbon steel, strength grade 8.8 (ISO 898-1)
Coating	SBZ – cold galvanizing 5–8 micron (ISO 4042) \| SBG – hot-dip galvanizing 40–50 micron (EN ISO 10684)
Technology	Structural expansion blind bolt
Sizes	M6, M8, M10, M12, M16, M20
Compatible sections	Square (SHS), rectangular (RHS) and circular (CHS)
Fire standard	Class A1 resistance per EN 13501-1
Characteristic shear (M20)	229 kN
Approval	European Technical Assessment ETA 25/0373 (April 2025), per EAD 330001-00-0602

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Strut Bolt structural blind bolt – installation and hollow-section connections.

Strut Bolt installation

Strut Bolt in a hollow section

Strut Bolt connection

Strut Bolt SBZ finish

Installation video

What is STRUTBOLT and how does it work?

When it comes to connecting to a hollow section – whether square (SHS), rectangular (RHS) or circular (CHS) – the problem is familiar to every engineer and installer: there is no access to the far side of the section in order to thread a conventional nut. Welding is possible but expensive and cumbersome, requires surface finishing, and is not always feasible on site. Ordinary bolts simply do not fit.

This is why blind-bolt technology was born, and ADIT's STRUTBOLT is its most advanced realization. It is a structural anchor for hollow sections, manufactured by the INDEX corporation and marketed exclusively in Israel by Adit Ltd., holding a European Technical Assessment ETA 25/0373 (April 2025).

Working principle: drill a hole of the appropriate diameter, insert the anchor from one side only, and tighten – first with an impact driver for initial locking, and then with a torque wrench for final closing. The tail of the anchor expands behind the inner wall of the section and creates a solid, rigid and secure grip – with no need for access to the far side and no welding.

Key technical features

Technology: structural expansion blind bolt for steel.
Raw material: carbon steel, strength grade 8.8 (ISO 898-1) – the leading standard for construction.
Available finishes: cold galvanizing (SBZ, 5–8 micron) or hot-dip galvanizing (SBG, 40–50 micron) for high corrosion resistance.
Available sizes: from M6 up to M20, capable of carrying enormous loads.
Compatibility: suitable for square, rectangular and circular sections.
Fire standard: fire resistance class A1 per EN 13501-1.

Why is the ETA standard so important?

The ETA is the most stringent and comprehensive certification for structural anchors in the world. It is granted by a recognized assessment body, following a series of in-depth, destructive tests of pull-out and shear forces, resistance under extreme conditions and more.

STRUTBOLT received approval ETA 25/0373 in accordance with EAD 330001-00-0602, which is intended specifically for expanding assembly systems for blind connection. For the engineer and contractor this means:

The nominal force values (pull-out and shear) are approved and verified by an independent European body.
The anchor is explicitly intended for structural and load-bearing connections – not only for light applications.
The values may be used for official structural design in accordance with Eurocode 3 (EN 1993).
The AVCP 2+ system ensures ongoing production control.

Worth knowing: in the Israeli market many competing products in this field do not hold a valid ETA. Choosing STRUTBOLT means using an approved product that provides professional backing, legal accountability and full compliance with the European standards.

Approved load values

Characteristic failure loads and approved design loads per ETA 25/0373. These are the officially approved values for use in structural design.

Anchor size	Pull-out N_rk [kN]	Shear V_rk [kN]	Design pull-out N_rd [kN]	Design shear V_rd [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 in accordance with Eurocode 3.

Comparison: STRUTBOLT vs. BOXBOLT BQ_S

For years the British BOXBOLT product was considered the gold standard in the field. The following comparison is based on the official performance data of the two products.

Size	BOXBOLT shear [kN]	STRUTBOLT shear [kN]	Advantage	BOXBOLT pull-out [kN]	STRUTBOLT pull-out [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 STRUTBOLT significantly outperforms BOXBOLT in shear, and in almost all sizes it is superior in pull-out.

Hot-dip or cold galvanizing? Choose the right protection

SBZ – cold galvanizing

Zinc coating of 5–8 micron (ISO 4042). Suitable for indoor environments – warehouses, industrial buildings and covered bridges. Excellent durability of over 50 years in a C1 corrosion environment.

SBG – hot-dip galvanizing

Massive zinc coating of 40–50 micron (EN ISO 10684). Intended for outdoor environments, coastal areas and heavy industry. Over 50 years in a C2 environment, and up to 47 years in a harsh C3 environment.

6 reasons to choose STRUTBOLT

Approved performance (ETA): all force values are officially approved by an independent European body, with no fictitious figures or "manufacturer estimates".
Single-sided installation: no need to access the far side of the section, no need to weld, and no need for a second person to hold a nut.
Compatible with all hollow sections: square (SHS), rectangular (RHS) and circular (CHS), for all common wall thicknesses.
Wide size range: from M6 for light connections such as billboards, up to the formidable M20 carrying 229 kN in shear, for primary structural constructions.
Major cost savings: welding requires a certified welder, paint finishing, non-destructive testing and cooling. STRUTBOLT requires only drilling a hole and a driver.
Durability and life cycle: strong 8.8 steel combined with the hot-dip galvanizing option ensures an engineering solution for half a century ahead.

Frequently asked questions

What is a hollow-section anchor and how does it differ from an ordinary bolt or a concrete anchor?

An ordinary steel bolt requires access to both sides in order to thread and tighten a nut. In a hollow steel section (SHS/RHS/CHS) – such as closed steel columns or rectangular beams – there is no access at all to the inside of the section. A hollow-section anchor (Blind Bolt) is designed so that it is inserted from one side only, and as it is tightened its steel mechanism deploys and expands behind the inner wall, locking the connection powerfully.

Why is a connection to an RHS/SHS section 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 galvanizing layer, may weaken the section due to heat, and then requires expensive non-destructive testing. Anchors such as STRUTBOLT bypass all of these problems by means of cold drilling and mechanical tightening.

What is the difference between STRUTBOLT and a Lockbolt?

Both are advanced fastening solutions, but they work differently. A Lockbolt usually consists of a pin and a collar, requires access to both sides or is used as a rivet for thin sheet plates, and works by one-off tensioning and swaging using a dedicated tool. STRUTBOLT is a true blind bolt intended for significant structural wall thicknesses, installed from one side only, and requiring only standard tools – a driver and a torque wrench.

Which anchor sizes are suitable for a hollow section?

The STRUTBOLT series is available in sizes M6, M8, M10, M12, M16 and M20. The choice depends on the calculated loads and the wall thickness of the section. Each size (and each length of the same bolt) has an allowable fastened-material thickness range (tfix). The technical data should be verified with ADIT's engineering team before ordering.

Can a hollow-section anchor be used for primary structural connections?

Yes, absolutely – as long as the anchor holds an approved European ETA as STRUTBOLT does (BWR1, mechanical resistance and stability). It can be used with confidence in primary structural connections and the loads can be designed per Eurocode 3. The design is always the responsibility of the structural engineer.

Can a chemical anchor be used instead of a steel anchor in a hollow section?

No. A chemical anchor is intended for anchoring within binding materials, stone or concrete, where it fills the drilled cavity and bonds to the walls. In a hollow steel-section connection there is not enough surface area for bonding and no base material to grip. Therefore a steel-to-steel connection in a closed cavity requires a mechanical anchor.

How much force can a STRUTBOLT M16 anchor really carry?

An M16 anchor carries a characteristic failure load of 101.5 kN in pull-out and 145.6 kN in shear – over 14 tons. The design loads (after a safety factor of 1.25) are 81.2 kN in pull-out and 116.5 kN in shear. These loads make it an excellent alternative to welding in heavy sections.

Do BOXBOLT and STRUTBOLT work on the same principle? Which is better?

Yes, both are expanding blind bolts installed from one side of the section and tightened with torque. In the past BOXBOLT was the industry default, but today INDEX's STRUTBOLT provides higher shear and pull-out data, carries a more advanced and up-to-date ETA approval (April 2025), and is offered at a competitive price with full availability in Israel through ADIT.

Can STRUTBOLT be used in a circular section (steel tube)?

Yes. STRUTBOLT is suitable for square, rectangular and circular sections alike. The only thing to check with a circular section is that the diameter of the internal cavity is wide enough to allow the anchor to open and deploy fully according to the specification.

Is a special tool required for installation? What is the required torque?

No. Unlike a Lockbolt, which requires an expensive dedicated hydraulic pulling tool, STRUTBOLT is installed with a standard impact driver for initial locking and a standard torque wrench for 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 required torque.

Can a STRUTBOLT anchor be dismantled and reinstalled?

No. The blind bolt works on a principle of irreversible mechanical swaging and deployment inside the hollow section. Once installed and tightened to the required torque it becomes a permanent connection. The central bolt can be removed to dismantle the external element, but the internal anchoring sleeve will remain locked inside the beam.

Is STRUTBOLT also suitable for dynamic loads and vibrations?

According to ETA 25/0373 the anchor is approved for design under static and quasi-static loads. For applications involving constant fatigue loads – such as lifting equipment or vibrating machinery – a structural engineer and ADIT's engineering team should be consulted in advance to verify applicability and safety.

Planning a connection to a hollow section? Send us the section, the wall thickness and the loads – our engineering team will match the right STRUTBOLT for you and send the ETA data.

Talk to our engineers