incl. 20% VAT
incl. 20% VAT
expansion bolt – also known as heavy-duty anchors – are an essential component when setting up climbing routes.
Firstly, they fix the bolt hanger to the rock.
Secondly, to put it simply, they bear the majority of the forces in the event of a fall.
And thirdly, the “bolts” transfer the loads to the bedrock as a so-called friction system.
Because of the way they are installed, they are sometimes also referred to as “impact anchors”.
Components expansion bolt
Below you will find a description of the components of a heavy-duty anchor. The definitions are very important. This is because they guarantee that we are always talking about the same components of impact anchors.
Mother
The nut ensures power transmission at donning. For 8mm expansion bolt an M8 nut is used. A 10mm bolt requires an M10 nut, etc…
Consequently, the correct wrenches must be used during installation. Please note the historical development of tool designations. An M8 nut requires a 13 mm wrench. The M10 nut requires a 17 mm wrench. And finally, the M12 nut requires a 19 mm wrench.
Washer
The washer fulfills several functions at once at expansion bolt.
Firstly, it ensures that the contact pressure is distributed over the entire nut.
Secondly, it ensures a flat contact surface on the ground.
Thirdly, it also acts as a (friction) buffer between the components. As a result, it helps to prevent damage to a zinc plated surface, for example. This means that the nut cannot “rub” directly on the bolt hanger, for example. This means that the surface remains undamaged. This applies to zinc plated components on the one hand. And on the other hand for stainless steel products with their protective “passivation layer”.
expansion bolt Thread
The thread is required to be able to fix the nut to the impact anchor. On the one hand, the length of the thread depends on the overall length of the bolt. On the other hand, it depends on the desired anchoring depth. The greater the anchoring depth, the smaller the thread.
A thread should protrude a maximum of 1.5 x the diameter from the substrate. Consequently, this is exactly 15mm for a 10mm expansion bolt. Once the desired component has been fitted, the following rules of thumb apply. Maximum protrusion = 6mm. Minimum protrusion = 3mm.
Is the protrusion significantly more than 6 mm? Then this indicates that the anchoring depth is too shallow. There is also a high risk of injury from the sharp thread heads.
Is the protrusion less than 3 mm? If so, the thread may break or shift. The nut may then no longer be able to be loosened.
Poorly positioned expansion bolt with far too much “protrusion”. As a result, this bolt has too little anchoring depth and is also a hazard due to the sharp edges. Photo: bolting.eu
Expansion links
Together with the cone, the expansion elements ensure the so-called frictional connection. This means that the force of turning is converted into lateral pressure. How well this works depends mainly on the surface!
When used in the construction industry, the decisive factor is the concrete quality. On the one hand, there are approvals for expansion bolt in non-cracked solid concrete. On the other hand, there are also approvals for cracked solid concrete. You can find more information below in this article.
But now to the Applications for alpine sports such as climbing. The type of rock is crucial here . On the one hand, gneiss and granite, as well as hard limestone, can be compared with non-cracked concrete. On the other hand, slightly porous limestone, tuff or solid conglomerate constitute cracked concrete.
Very soft rock types such as sandstone or marl are not suitable for heavy-duty dowels. Here glue in bolt must be used!
Cone
Together with the expansion links, the cone-shaped cone ensures the frictional connection of the expansion bolt. This is because the cone pushes over the expansion links on a firm surface. As a result, this process converts the energy of donning into lateral pressure. This friction ensures the hold of the impact anchor.
There is therefore an ideal force for each bolt donning. The so-called torque. When installing a bolt, you should always know the appropriate value. This prevents “overtightening”. Because if a heavy-duty bolt is donned too tightly, it can break!
As a rule of thumb: If you hear the clear “clack-clack” sound of the expansion links “breaking open”, the torque is approximately correct.
You can find more details on the torque further down in the article!
Screenshot from the fischer.at website. Applications and approvals for Fischer FBN II 10/10 A4 steel;
expansion bolt Approvals
Several sources of information provide information on the approval of an impact anchor.
Manufacturer website
Here you should find one or all of the following documents for each manufacturer:
ETA approval
European Technical Assessment. This means approval by a certified testing institute. Our supplier Fischer, for example, tests at the German Institute for Building Technology.
Exemplary download: ETA approval of Fischer FBN II 10/10 A4 steel
DoP Declaration: Declaration of Performance
“Quasi” the manufacturer’s operating instructions for the impact anchor. It must contain all important product details. The DoP declaration must also be checked by a certification body.
exemplary download: DoP of the Fischer FBN II 10/10 A4
Data sheet / technical sheet
Information from the manufacturer about the product, usually provided as a pdf download.
Product information – Manufacturer website
Here you will always find information on the approvals!
Original packaging
The original packaging also provides essential information on applications and approvals.
The original packaging provides very important information about the expansion bolt and should always be available! Photo: Bolting.eu
Important reverse conclusion!
“Loose” expansion bolt without detailed information is a very bad idea! Products without information on the manufacturer, type, steel quality and approvals are bound to have processing errors! The same applies to gaps in the construction documentation (legal risks) and, in most cases, galvanic corrosion.
Torque at expansion bolt
Every heavy-duty dowel has an ideal force with which it should be donned. This force is called the torque. You will find this value on the original packaging and in the operating instructions. It can also be found in the ETA and DoP declaration.
The exact torque can only be determined with a torque wrench.
Torque wrench
The impact dowels can be donned precisely with the help of a torque wrench!
As a rule, the following values apply to zinc plated or stainless steel bolts:
8mm: 15-20 kN
10mm: 20-30kN
12mm: 45-55kN
The entire explanation would go beyond the scope of this article. You can therefore find all the detailed information on this topic in our technical article“Torque at expansion bolt“!
Consequences of the torque
Donning a expansion bolt too tightly causes two things to happen.
Material tension
Firstly, it places the component of the impact anchor under increased tension. This is extremely disadvantageous! On the one hand, fractures due to excessive torque have already been documented in climbing routes. On the other hand, stress corrosion cracking is pre-programmed in the corresponding environments (salts, temperature, humidity).
Breakout cone
Secondly, the force is transferred laterally to the rock or concrete. This is the so-called blasting effect. There is a very typical break-out pattern here, also known as the “break-out cone”. This cone is 1.5 x the anchoring depth wide. In other words, in reverse:
expansion bolt must be set at least 3 x the anchoring depth apart! This is essential, for example, when installing lower offs, abseiling points and top rope points!
You can find all the detailed information on this in our technical article“What do expansion bolt hold?”
Steel qualities for expansion bolt
Heavy-duty dowels are available in many different steel grades. We would like to briefly present the five best-known grades here. We have also listed both the advantages and disadvantages. We also indicate firstly whether the steel quality is compatible with the EN 959 standard. Secondly, whether it can be used for climbing frames. Thirdly, whether the bolts can be used near the sea.
Steel qualities for expansion bolt
Steel quality
Advantage
Disadvantage
EN standard 959
compatible
Suitable for climbing frame holders
Proximity to the sea
zinc plated
inexpensive
Low steel quality
❌
❌
❌
A2
inexpensive
Steel quality not optimal
✅
❌
❌
A4
Corrosion resistant
Price
✅
✅
❌
Fixed PLX steel
Corrosion resistant
Price
✅
✅
✅
HCR steel
Highest steel quality
very expensive
✅
✅
✅
Zinc plated bolts
Zinc plated impact anchors are inexpensive. However, they have the shortest service life of all steel qualities. This is because they are “only” standard ferritic steel that has been galvanized zinc plated.
Furthermore, they are not suitable for official climbing crag holders. Consequently, we only recommend these bolts for temporary belay points.
A2 steel heavy duty anchor
These expansion bolt are an inexpensive alternative for many “private developers”. This is because it is already a higher quality austenitic steel. A2 is already referred to as stainless steel.
In principle, there is no reason not to use it in the Alpine region, especially in primary rock. Disadvantages arise when used in limestone. This can lead to shorter life spans. This is because various limestone components (e.g. magnesium) can contribute to the formation of corrosion-promoting salts.
A2 steel is no longer generally considered to be of sufficient quality for official climbing areas!
A4 steel expansion bolt
Certainly THE standard for climbing areas in the Alps. A4 steel is often referred to by the American standard AISI 316. The low-carbon variant AISI 316L is also very common. This chromium-containing steel has a very long service life due to its protective passivation layer.
Fixed PLX steel
Heavy-duty anchors made from this steel have very high corrosion resistance. They are also highly resistant to stress corrosion cracking and pitting. This property is based on the one hand on the crystalline structure of this so-called “duplex steel”.
Consequently, duplex steel can also be used for bolting near the sea. It is currently the only affordable alternative. At € 3.99, fixed PLX impact dowels are around twice as expensive as A4 expansion bolt!
Want to know more about the PLX / Duplex steel? Here you can find all the details about the Fixe PLX / Duplex steel!
HCR steel
This steel grade is also known as AISI 901L steel. Heavy-duty anchors made from this material are extremely resistant to corrosion. This goes hand in hand with an extreme price of around € 20 per piece!
As a result, HCR steel has not yet gained widespread acceptance. Unsurprisingly, given the high costs.
For climbing areas near the sea, only PLX / duplex steel and HCR steel are suitable in the long term. Titanium is not steel, but is also an extremely corrosion-resistant material. Photo: bolting.euWould you like to find out more about steel qualities? Then we recommend our technical article“Steel qualities at expansion bolt and glue in bolt”
Steel quality is crucial for climbing garden supports!
Anyone who officially maintains a climbing area in Austria is referred to as the “climbing area operator”. They are responsible for a wide range of duties for the established routes. These include ensuring adequate safety.
The valid “traffic standard” is the EN 959 – UIAA 123 standard.
In simple terms, this means the following: All belay points must be made of corrosion-resistant stainless steel. Consequently, it is essential for climbing garden owners to know about the steel qualities at expansion bolt. This is because the correct heavy-duty anchors must be used. As well as the right bolt hanger and lower off climbing anchors.
Zinc-plated expansion bolt and bolt hanger are immediately recognizable in limestone due to the distinctive white stripes. We strongly advise against mixing zinc-plated and stainless steel fixed points because they are simply not standardized for official climbing areas. Photo: bolting.eu
EN Standard 959 / UIAA 123 Compatibility
With this standard, steel quality A4 has emerged as the new traffic standard. This means that an average responsible climbing garden owner will not use a steel grade lower than A4 for the belay points. This grade of steel is therefore considered suitable for expansion bolt in official climbing areas.
We therefore urgently recommend that all climbing garden owners. Only use heavy-duty dowels of A4 or higher quality. Both for climbing area construction, climbing area rebolting and climbing area maintenance. In addition, we advise without exception to provide appropriate construction and maintenance documentation. In this way, legal risks can be avoided.
More legal information can be found in the manual for climbing areas of the province of Tyrol!
Galvanic corrosion with expansion bolt
This phenomenon occurs when components of different steel qualities are used.
For example, zinc plated bolts with stainless steel lugs or nuts. Put simply, electrons migrate from base metal to precious metal. In doing so, they cause corrosion. Depending on the general conditions, this can weaken the base metal component relatively quickly. In extreme cases, this can lead to breakage.
Classic example of galvanic corrosion at expansion bolt. A stainless steel lug with stainless steel nut was screwed onto a galvanized zinc plated 10mm bolt. Photo: bolting.eu
Prevention of galvanic corrosion
This widespread problem has many causes. We would therefore like to highlight the most important points below and raise awareness.
Unconscious mixing of steel qualities
The most important rule is. Only use components of the same steel quality! I.e. A4 heavy-duty dowels only with A4 / AISI 316L lugs. PLX bolts only with PLX lugs. Etc…
Unfortunately, some developers are not familiar with the principle of galvanic corrosion. That’s why this rookie mistake still occurs.
Bottle refilling
We’ve all been there. A bolt hanger is missing on a climbing route. The next available bolt is quickly taken. Just like any washer and nut. Everything is quickly fitted. Done!
Unfortunately, however, this again ignores the fact. All parts must have the same steel quality! The result? Galvanic corrosion again!
Bottle storage
A practical tip from our decades of experience. Always store your impact dowels by type. I.e. 1 steel grade in 1 box. If necessary, you can also mark them accordingly. If you are unsure what a component is made of? Always throw it away!
Want to find out more about this important topic? Then read our technical article“Galvanic corrosion at expansion bolt“!
expansion bolt Attachment
The following video shows the correct attachment of a fixed point in a climbing route. The use of a torque wrench is unfortunately not common in practice. Just be careful not to donning the nut of the bolt too tight. Just listen for the clear “click-click” sound of the expansion links!
The values for installation are 10/10 for the Fischer FBN II, for example:
30Nm for zinc plated steel
20Nm for A4 steel
Consequently, the A4 steel expansion bolt in particular must not be “overtightened”! Avoid this classic rookie mistake during installation.
Further installation information
Are you looking for a detailed description of bolting a climbing route? That would go beyond the scope of this article, so here are some links. There you will find detailed instructions and pictograms!
to bolt a climbing route
Set up a climbing route with expansion bolt
Download installation instructions for expansion bolt
8mm, 10mm or 12mm expansion bolt?
One of the most frequently asked questions we receive is: Should I use an 8mm, 10mm or 12mm bolt for climbing routes?
We therefore want to answer this question in a practical way here.
8mm expansion bolt
Although they can already withstand decent breaking loads, they are not suitable for official climbing areas. The standard specifies at least 10 mm heavy-duty anchors for these “official” routes.
Nevertheless, 8mm bolts are still often used in alpine terrain. On the one hand, this is due to the low weight of the impact dowels and lugs. And on the other hand, the low battery power required to drill the holes. Anyone setting up a 300-400m route in alpine terrain will appreciate the halving of their weight!
8mm expansion bolt in speleology
Speleologists are among the most frequent purchasers of 8mm bolts in our store. Consequently, they are extremely common and popular in speleology. And for the same reasons as mentioned above. Firstly, the low weight. Secondly, the low battery energy for the drilling hole.
In addition, the relatively low loads (no falls!) when caving are another argument in favor of the economical 8 mm version.
8mm for slacklines?
Due to the sometimes very high forces involved, we strongly advise against this. Especially pretensioned lines without slack require very strong, redundant protection. 8mm impact anchors are definitely not suitable for this!
10mm expansion bolt
Even 10mm heavy-duty dowels achieve enormous breaking loads. These are beyond 20kN. This means that these forces cannot be achieved in the event of a fall! (Note: assuming correct processing!)
Consequently, the diameter of the impact dowels is usually not the decisive factor. Rather, the quality of the rock substrate is decisive.
This means that 10 mm bolts are completely sufficient for the forces that occur during climbing! (Note: with sufficient anchoring depth)
This is also made clear by the corresponding EN 959 standard. This specifies the following breaking loads for the material AND (!) for the substrate:
15 kN in axial direction
25 kN in radial direction (UIAA 20 kN in axial direction)
Consequently, make sure the rock is firm and compact. This is done by systematically “tapping” the bedrock. Solid rock produces a high, “firm” sound. Hollow rock produces a deep, “dull” sound.
The required strength is often not achieved in hollow rock. The rock simply breaks if it is too bad (see “break-out cone” above!)
12mm expansion bolt
We recommend 12mm heavy-duty dowels for high static loads. For example, slacklines and flying foxes as well as training stands for mountain rescue services. Here, 12mm bolts with corresponding anchoring depths make perfect sense. The lengths must be adapted to the nature of the rock substrate.
Moreover, in our opinion, this dimension makes sense for cave rescue. Here, high static loads occur in many variants. For example, with horizontal ropeways or when several people are hanging from a fixed point.
The differences in the dimensions of the standard expansion bolt sizes clearly show the different areas of application. Graphic: bolting.eu
Practice tips
Below we give you some cool practical tips on the subject of expansion bolt.
Overdrilling
The holes when setting your expansion bolt should be at least the same length as the bolts. We even recommend drilling 1 cm deeper. This way, the hooks can simply be hammered in if necessary and do not have to be painstakingly removed!
Use material bags
Use a material bag like the Beal Tool Bucket when bolting. Pre-assembled heavy-duty anchors including a lug on a carabiner are a bad idea. They rotate very slowly when working in the wall and the bolts will eventually just fall out of the lugs!
Use the right drill bits
We recommend SDS drill bits with PGM test mark for your cordless rotary hammer. This guarantees the “cutting corner dimension”. This means round holes into which the bolts can be hammered perfectly.
