Fastener Technology

Many companies that have been designing with inch (imperial) fasteners for years are very hesitant to switch over to metric. Why would anyone ever use metric hardware? Where we have seen the most interest is from companies who are expanding into global markets. Most countries other than the US are using metric fasteners and for them, imperial fasteners are a mystery.

Metric is simple once you get the hang of it, and some things even make more sense, such as the marking of property classes (grades) on nuts and bolts. The metric system uses numbers stamped into the head or face of the nut rather than symbols that we use for inch hardware. For bolts, the first number indicates the strength in MPa while the second number tells us the percentage of yield strength.

For example:

Property class 10.9 – 10 indicates a tensile strength of 1000MPa, 9 indicates that the yield strength is 90% of tensile.

Property class 8.8 – 8 indicates a tensile strength of 800MPa, 8 indicates that the yield strength is 80% of tensile.

Metric Fasteners Chart

A quick comparison of grades and property classes is shown below:

If you are considering a conversion to metric hardware, contact Bossard at ProvenProductivity@Bossard.com, or check our technical resources at www.bossard.com including an inch to metric calculator that is also available as an iPhone app.

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Doug Jones
Applications Engineer
Email: djones@bossard.com

Coarse threads have become the standard for most fastener applications, but when should fine threads be considered?

Fine Thread Strengths

Fine threads are technically stronger under static loading, because they have a larger minor diameter which translates into a larger cross-sectional area A_s. If using fine threads to increase strength, it is important to make sure that the mating thread – the nut or tapped hole – can support the additional load. This may require a thicker nut or more thread engagement in a tapped hole. Remember the cardinal rule that the nut member must always be stronger than the bolt!

Fatigue Resistance of Fine Threads

In joints with high cyclical loading, fatigue failure becomes a concern. Repeated cyclical stress can create cracks which typically occur in the first loaded thread of the joint. Studies have shown that fine threads increase the percentage of load on the first thread, which can lead to a shorter fatigue life. In this scenario, fine threads should not be a first choice.

Fine Thread Vibration Resistance

In the past, vibration resistance was thought to be a benefit of fine threads. The smaller helix angle, at least in theory, slows down the loosening process. A tradeoff of this benefit is the slower assembly time of fine threads; the smaller helix angle requires more angle of rotation to advance, slowing down the assembly process. A better solution to vibrational loosening can often be found in some sort of locking mechanism which can be recommended by your fastener source.

In conclusion, fine threads should not be used for load bearing joints unless there is a very specific reason and testing is done to validate the joint. Some exceptions could be hard to tap materials or thin wall materials. For non-load bearing joints that require adjustment, fine threads may be your best option.

For more help on choosing the proper fasteners for your project, contact us through ProvenProductivity@bossard.com.

Doug Jones
Applications Engineer
djones@bossard.com

Hydrogen embrittlement is a permanent loss in ductility caused by introducing hydrogen into a metal fastener in combination with stress. A typical hydrogen embrittlement (HE) failure is a delayed failure and happens after assembly. An HE failure is caused when three requirements are fulfilled. These areas are (1) hydrogen induced, (2) stress applied, and (3) high hardness. Continue reading for more information about each area.

Hydrogen Induced

Hydrogen needs to be induced for an HE failure. This is most commonly induced in the electroplating process, but can also be introduced into the material through corrosion of the bolt.

Stress Applied

Once stress is applied to a bolt that has a significant amount of hydrogen trapped inside the molecular structure, it is a matter of time when the hydrogen collects in molecular void and that void will grow bigger until the fastener fails.

High Hardness

This is the easiest pillar of an HE failure to control in the HE failure spectrum. Industry standards dictate that anything 320 Vickers Hardness or higher needs stress relief and possible further special attention.

HE failures can be very dangerous because the failure is delayed after installation and is very sudden. Before a bolt with HE is installed, there is not a visual way to identify if HE is present.

Any fastener that meets the hardness criteria need special attention and care to avoid HE failures. Contact us at ProvenProductvity@bossard.com if you have any questions about HE and its causes.

Brandon Bouska
Application Engineer
bbouska@bossard.com

The use of captive nuts is a great design opportunity for a variety of applications. These differing styles of nuts are captive because once installed, they become an integrated part of the assembly. Examples of captive nuts are weld nuts, self-clinching nuts and riveting nuts. For more information on the specific designs consider the technology of each one.

Weld Nuts

Weld nuts are welded to another piece of metal. These can be used instead of sheet metal screws in thin sheet metal applications. Weld nuts come in different sizes and shapes and require equipment to install. These types of nuts form the strongest bonds. They are not plated for corrosion protection as this would hinder the welding process; a subsequent plating process or painting would be required to protect the assembly from corrosion after welding is complete.

Self-Clinching Nuts (swage nuts or insert nuts)

Self-clinching nuts are clinched or pressed into soft sheet metal. They come with several types of plating options and can be heat treated to provide more thread strength unlike its counterparts. Self-clinching nuts also require equipment to install.

Riveting Nuts (blind rivet nuts)

Riveting nuts are the quickest to install. The necessary tools to implement this nut design are also relatively less expensive. They are installed much like a blind rivet and can be fixed into blind holes unlike self-clinching nuts or weld nuts.

Captive Nuts Comparison Chart

**Advantages and disadvantages are accurate for most catalog offerings of these nuts, exceptions may apply

Picking the right captive nut for your design can be difficult. Luckily, Bossard has an engineering team with decades of experience, ready to help you. Contact us at ProvenProductivity@Bossard.com for more information.

Fadi Saliby
Technical Sales Director
FSaliby@bossard.com

The lighting industry benefits from modern advancements in the smallest details of engineered lighting components. Rivets and fasteners, as well as wire management products, help everyone with their lighting needs. Whether the requests are for residential electrical jobs or those industrial and institutional lighting projects, the industry is thriving with several options for each scenario.

Rivets and fasteners are a few components that offer creative solutions to many lighting necessities. Drive fasteners, mounting buttons, fastener plugs and push-in fasteners are all a part of successful lighting installations. They can ensure a successful installment of light fixtures with convenience in mind.

Wire management is another concept to be appreciated when stringing it all together. Cable clamps will be a beneficial factor in keeping wires and cables neat and organized. A variety of clips and clamps exist in the markets today that are customized for those very specific jobs at hand.

The lighting industry has come a long way in making the little things matter more. The technological benefits and enhanced features that have been implemented in the smaller aspects of lighting are making more lighting preferences possible.

Reach out to us at ProvenProductivity@Bossard.com to see how Bossard can help you with your lighting fastener needs.

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When designing a bolted joint, many engineers look to a library of current designed-in parts, which is a great practice and should always be the first step when selecting possible fastening components. Many times, a part gets selected based on the dimensions of the fastener and is chosen for that reason alone. If the fastener’s finish is overlooked, it could be outperforming its requirements with regards to the finish. Basic knowledge of plating and coating practices can help create cost effective designs.

In one example, a bolt already in one customer’s fastener library had a finish designed for a corrosive environment. The finish standard limited that particular finish to one applicator. Without a basic knowledge of finishes, it is difficult to understand the consequences of requiring a bolt to use such a restricted supply base. After reviewing the example application, a suggestion was made to change the finish on the fastener to a coating more readily available in the industry. This suggestion resulted in a cost savings of over $30,000 per year.

A basic understanding of any implemented coating could help reduce initial cost of the bolted joint and will help the designer create a cost-effective design.

For more information on how you can create a more cost-effective bolted joint design, contact us at ProvenProductivity@bossard.com.

Brandon Bouska
Application Engineer

It is not uncommon for fastener manufacturers to adopt an SOP (standard operating procedure) and perform final inspection of the product after it is completed.

Do you believe final inspection is the best detection method?

Not always. If the product was contracted out of the manufacturers facility for heat treatment, patch, coatings or sorting, many things can potentially happen when the product is shipped out for further processing that the manufacturer cannot control. Product may be damaged, mixed with other types of product, or missed critical processes such as heat treatment or baking requirements. At minimum, all containers received back from outside services should go through a thorough visual inspection, and the certifications received back from contractors should be reviewed, as it is important to understand them.

So how many processes are there to make a simple hardened hex head cap screw with a patch?

Typically, there are manufacturing drawings created by an engineering group that are then reviewed and officially released for production. Wire is then ordered, sometimes delivered in a raw state, then cleaned, pickled, and drawn to a specific diameter. When completed, off to production:

• Heading/Forming
• Cleaned
• Thread Rolling
• Secondary (drilling/turning/milling/straightening), if applicable
• Heat Treatment
• Surface Treatment
• Patch Application

So which process is most important?

They all are! If a non-conformity is not detected “in process”, the manufacturer will invest more time and resources in further processes, and hopefully detect the non-conformity during a final sample inspection, or even worse, at the customer.

Contact us through ProvenProductivity@bossard.com, and find out what robust quality processes we encourage Bossard manufacturers to practice to ensure good quality fasteners for our customers.

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Tony Peters
Quality Manager