A forum about optimizing
bolt securing

Tips and tricks: How to optimise a bolted joint through clamped length

First published in Bolted #1 2017.

Q: What is clamped length?
A: Clamped length – LK – is the free length of a bolt that is stretched under tension, meaning:

  • In a through hole (A), the distance between the bolt head and the nut.
  • In a blind hole (B) – or for a stud bolt (C) – the distance between the head (nut) and the first thread engaged in the tapped hole.


It is also called “grip length” as the total thickness of clamped parts under compression.

To optimise a bolted joint, it is recommended to design the clamped length to at least 3 or 5 times the bolt diameter. Increasing the elasticity of the fastener greatly improves the properties of the joint, as it:

  • Increases the elongation of the bolt, reducing settlement effect.
  • Increases the flexibility of the fastener, reducing the risk of self-loosening under vibrations and transverse loads.
  • Improves the load factor, reducing the amplitude of dynamic stresses in the bolt and minimising the risk of fatigue failure.
  • Minimises the load transfer loss in case of hydraulic tensioning.


For stiff joints that don’t permit a long clamped length, it is possible to implement smart and effective solutions to avoid failure. Instead of using expensive and unattractive spacers, you can, for example, use:


Do you have a question about bolt securing?
Put the Nord-Lock experts to the test.
Email your questions about bolt securing to


Video: Nord-Lock washers Junker vibration test

Video: Superbolt multi-jackbolt tensioners

Download: Nord-Lock washers CAD files

Nord-Lock Group keeps the railway industry on track

First published in Bolted #1 2017.

Starting with ROLLING STOCK some 20 years ago, Nord-Lock wedge-locking washers are now found in all safety-related areas of the railway industry, such as bogies, coupling devices, brake systems, rail dampers, housing, and many more.

Nord-Lock washers ensure the functionality of bolted joints, even at the highest levels of vibration caused by rail traffic. One example is in railway switches, highly complex structures that must be used as long as possible with minimal maintenance, while exposed to the elements and to considerable stress.

Nord-Lock steel construction washers (NLSC) help railway companies avoid operational downtime, thus saving money. When renovating or replacing old bridges, small temporary bridges are assembled on site with a bolt preload of 100 percent to achieve secure bolted joints. However, these bolt connections can only be used once. Using Nord-Lock washers, the preload can be reduced.

Overhead line masts and signal masts must cope with severe dynamic loads caused by passing trains. Given the large number of masts, reliable bolt connections are crucial to reducing maintenance costs. With their special geometry, Nord-Lock X-series washers increase security, including on bolted joints with short clamp length, as well as in softer materials.

A recent application for the Nord-Lock X-series is noise-absorbing walls, which cope with extreme vibrations from passing trains. In Germany alone, 3,000 km of noise-absorbing walls are to be installed by 2030. A combination of concrete bolts and X-series washers is used to attach noise-absorbing barriers on existing bridge decks, many of which were not designed for noise barriers.


Video: Nord-Lock washers Junker vibration test

Video: Multifunctional Nord-Lock X-series washers

More: Nord-Lock Group solutions in the Railway industry

How the Expander System Group came to life and evolved

12 July 2017

Text: Ulf Wiman

photo: Stefan Jerrevång

The Expander System Group, the latest Nord-Lock Group acquisition, shares many customers with its new parent company and their history is remarkably similar. Founded in a remote part of Sweden, evolving from an innovative idea. In Expander’s case, a rusty nail was transformed into market-leading pivot technology. Founder and former owner Roger Svensson tells the story.

First published in Bolted #1 2017.

What is Expander’s business?
“Our patented Expander System is a state-of-the-art, cost-effective solution that permanently ends pivot wear in construction, forestry, mining and other heavy machinery. Fitted in the pivot, a double-locking expanding pivot pin assembly increases stability and safety and eliminates welding and line boring of worn-out pivot lug ears. The system has been field-tested for over 50,000 hours without failure.”

How did the company start?

“My father, Everth, and his twin brother Gerhard, did road work in the 1950s, starting out with one bulldozer. Machinery joints and pivots are prone to wear and tear, leading to expensive downtime and repairs, but they came up with a makeshift solution, knocking a rusty nail into the lughole to eliminate the gap. This worked surprisingly well, which inspired them to start developing the technology.”

When did you get involved?
“I learned about their ideas and immediately saw the potential. My father and I founded the company in 1986. At quite an early stage we got involved with computer engineers in the development of a parameter-controlled CAD system. This is an invaluable tool, as each Expander System is custom made to fit customer-specific applications.

In the 1990s we expanded geographically. North America is a huge market and in 1997 I moved there to get a business foothold. The launch was successful and in 2006 we established our own production facility in North America.”

Why did you sell the company?
“Enormous markets, such as South America, are starting to develop, but you need local presence. It was about either setting up my own network or selling to someone that already had a global subsidiary and distributor network. We already collaborated with Nord-Lock and after several discussions with Ola Ringdahl, CEO, Nord-Lock Group, I was sure that the Nord-Lock Group was a perfect fit.”

What does Expander bring to the Nord-Lock Group?

“There has been a major change in how people view repair and maintenance, which makes the market potential for the Expander System huge. We’ve only scratched the surface.

Also, we and the Nord-Lock Group have often shared customers, but solved different problems. Bringing our solutions together – and cross-fertilising them – will make our portfolio and product range so much stronger, which will benefit the customers.”

Facts: Roger Svensson
Role: Founder and former CEO, Expander System Group.
Age: 56.
Lives: Sedona, Arizona, USA.
Background: Studied Economics/Political Science at UCLA (double major). Member of the UCLA team that won the prestigious NCAA swimming championships in 1982. Held a couple of positions with other companies before starting Expander with his father in 1986. “I have always been an entrepreneur.”
Passion: Music: sings, plays guitar and writes his own songs. Is currently working on his debut album. Also paints and likes to write.

Washers keep airplanes in the air

First published in Bolted #1 2017.

Look up into the sky in the coastal city of Miri, in north-eastern Sarawak, Malaysia, and you may see Nord-Lock washers in action: inside a radio-controlled aircraft. These hobby airplanes are sold by Byond Horizon, a business that otherwise uses drones to take aerial photos and videos for companies.

“Unlike our drones, these recreational aircraft use gasoline-powered engines,” says Mr. M. Fadzly of Byond Horizon. “These engines cause a vibration problem. Since the frame is made of wood, which is soft, and the engine and its mounting are made of steel, the bolts holding them together can come loose after only four or five flights.”

Fadzly says that it can be difficult to access the plane’s engine, so the loosening is a real problem. A friend of Fadzly’s, however, works at Mayura Engineering and is a supplier of Nord-Lock washers.

“I ordered a box, tried them out, and now I recommend them to all of my customers when we are assembling their airplanes,” says Fadzly. “The Nord-Lock washers never need to be retightened, and they also make sure the engine stays in place. It would be quite dangerous if the engine were to fall out during flight.”

Fadzly not only sells the radio-controlled airplanes, he flies them himself. “I’ve been doing it since 1997,” he says. “It’s a passion, and a fun thing to do on the weekend. It gives you the feeling of flying a real airplane.”

►► Contact us to receive more information about Nord-Lock washers

Boltight subsea hydraulic bolt tensioners

Boltight manufactures both standard and custom built tooling for subsea applications. The subsea tensioners incorporate components that helps to save installation time, cost efficient, protects the environment and conforms to the requirements of the European Pressure Equipment Directive.

All subsea tensioners are assembled, filled with oil and have been pressure tested before dispatch. Boltight subsea tensioning tool is supported by a range of ancillary equipment such as high volume pumps, diver control valves, long length down line and hose reels.

Click here for more information about Boltight

Request for more information about Boltight

No downtime with innovative pivot pins

15 June 2017

Text: Alastair Macduff

photo: Rambooms

First published in Bolted #1 2017.

Customer: Rambooms
Range: >40 models from 450 kg to 20 tonne
End-customers: Crusher manufacturers and mines
Product used: Expander System Pivot Technology
Applications: Breaker boom systems

Rambooms Oy is a global supplier of breaker boom systems to crusher manufacturers and mines. Based in Finland, its products are used to break oversized rocks.

Pivot wear on these applications is a natural occurrence through time and repeated use, and the company had previously been using its own solution to prevent this. This solution, with a basic conical locking, had caused some issues. Rambooms’ own pins also arrived at its factory in pieces rather than assembled, which meant extra repacking work for personnel when sending the pins on as spare parts.

In 2009, the company took the decision to test the Expander System pivot technology and has been extremely satisfied with the results. The Expander pivot pins are already fully assembled when they arrive. This represents a significant time and cost saving in a competitive industry. Technicians have found fitting and locking much easier than the company’s previous solution.

The Expander System has offered Rambooms significant peace of mind, as it has had no customer issues with pivot wear since the company employed it. A marked improvement in delivery times has also been noted, as Expander always has the stock ready to ship.

“Our customers recognise the fact that the Expander pivot technology means good quality. This reflects well on us and our business,” says Samppa Varhomaa, Product Manager at Rambooms Oy.

The Expander System is locked into the pivot on the machinery when fasteners are tightened. The double-sided locking increases safety and stability, while both fitting and dismantling is simple.

Lubrication: The when and why for tensioning

8 June 2017

Text: Amaris Neidich & Joseph Vernam

First published in Bolted #1 2017.

Q: How does lubrication affect hydraulic tensioning and multi-jackbolt tensioning?
A: With the traditional method of tightening a nut, using a spanner, lubrication is very important, as there are a lot of surfaces moving against each other – the threads of the nut against the threads of the stud and the underside of the nut against the surface of the joint. Overcoming these frictional forces accounts for approximately 90 percent of the work (energy input) applied to generating the load in the joint.

When a hydraulic tensioning tool applies a clamping load to a joint, lubrication has no effect as it is applied directly to the stud and joint. A tension force is a linear force applied in an axial direction, so there is no rotation required to generate the load. This allows the nut to be turned down against the joint face under minimal friction.

As there is no friction to consider, there is no need to reduce the coefficient of friction using lubrication. Also, the lack of friction in the application permits much more accurate and repeatable results.

With multi-jackbolt tensioners (MJTs), the use of a lubricant on the main bolt thread does not affect the preload. It is advisable to use a very light film of lubricant with anti-seize characteristics to facilitate tensioner removal.

A more tangible effect of lubrication for MJTs is from the required lubricant use on the individual jackbolt threads, jackbolt bottoms of the tensioner, and washer face.

Proper use of lubrication is crucial to safeguarding repeatable and precise preload control in Superbolt installations. Superbolt mainly uses a graphite-based lubricant with a low friction coefficient and steady performance to achieve a positive impact on the preload. The MJTs are delivered with lubricant pre-applied to the installed jackbolts. Additional lubricant is included for application to the jackbolt bottoms. For subsequent installations, reapplication of lubricant is required to provide the intended performance.


Do you have a question about bolt securing?
Put the Nord-Lock experts to the test.
Email your questions about bolt securing to

Converting sea wave motion into energy

CorPower Ocean harvesting energy in the sea

First published in Bolted #1 2017.

ENERGY. With oceans covering more than 70 per cent of the earth’s surface, wave power is potentially a huge untapped source of renewable energy. The problem is that most wave energy converters are too large and costly to be commercially viable. Swedish company CorPower Ocean could have the answer.

The company’s compact Wave Energy Converter works by oscillating in resonance with waves, amplifying their motion and then converting that energy into power. CorPower Ocean founder, cardiologist Stig Lundbäck, invented the initial concept based on the pumping principles of the human heart. In the same way that a heart uses hydraulically stored energy to form back in place, the Wave Energy Converter uses a pneumatic pre-tension system to pull down the buoy after it has been lifted by a wave.

This allows for a relatively small device to harvest a large amount of energy. It is estimated that one buoy, eight metres in diameter, can generate around 250 kilowatts of power. That is enough electricity for around 200 homes.

“If you look at wave energy potential, somewhere between 10 to 20 percent of global electricity consumption could be provided by wave power,” says Patrik Möller, CEO, CorPower Ocean. “It has the potential to become the most competitive source of renewable energy. It offers five times more energy density than wind and ten times more than solar power. Waves have fewer variations and are more predictable than sun and wind, so you know a few days in advance what the energy flow will be.”

Currently, the Wave Energy Converter is undergoing tests with simulated wave loading, while a full-scale demonstration is being set up to begin in 2017. One of the key challenges has been keeping the buoy small and lightweight, while at the same time strong and durable enough to survive the toughest storms at sea.

This has presented a number of fastening challenges. On the mainframe inside the buoy, Cor­Power Ocean has elected to use Superbolt ­tensioners due to their lower torque requirements compared to a single bolt, which makes assembly far more manageable. Superbolt can also guarantee reliability over the buoy’s intended 20-year lifespan. At the base of the buoy, Nord-Lock washers are used, since they can maintain the correct tension over many load cycles over a long period of time.