Fastener Technology

Locking Fastener Methods to Secure Your Applications: Additional

Locking part 5

Part five of our series on fastener locking methods will focus on some alternative locking methods not previously covered.

Serrated Flange Nuts/Bolts

Serrated flange nuts and bolts use serrations on the bearing surface to create higher friction and prevent loosening, primarily on sheet metal joints. Care must be taken to NOT use any washers with this hardware and to ensure serrations on both the nut and bolt to prevent any rotation. When designed correctly, joints using serrated hardware perform very well, but corrosion can be a concern if the hardware is installed after paint as some material can be removed during assembly and especially if removal is required.

serrated flange nuts and bolts







Double Nuts

Use of a jam nut (or thin nut) to “double nut” a joint has been around for many years, and can be a very effective method of locking a threaded joint. The assembly method and the use of two nuts for each joint may not be the most efficient, and many people do not install them correctly. When using a jam nut, the thinner nut goes on first, and the standard nut gets tightened to full torque on top, while holding the jam nut in place. This can make it tricky to induce the proper pre-load on the joint which is part of the reason this method is seldom used any more.

double nuts







Mechanical Thread Locking

Some manufacturers have come up with special thread geometry to create a mechanical locking in either the internal or external threads. Different from locking nuts, which starts with a standard thread, and deforms or damages it to create friction, these specialty threads are rolled or tapped into the fastener when the threads are initially formed, which provides greater consistency and a more predictable clamp load.

Tab Washers

Tab washers have multiple tabs which are bent both in opposing directions after assembly to lock the nut or bolt head into the mating surface.

tab washers







Castle Nuts

Castle nuts or slotted nuts have slots cut or formed across the flats to allow for a cotter pin to be passed through a cross drilled hole in the mating male threaded component. Often used on highly critical joints such as front wheel bearing assemblies on automobiles, this positive locking feature is a guaranteed, but costly way to secure a bolted joint.

castle nuts






Safety Wire

Generally used in aircraft, high performance automotive, or other high critical applications, these bolts and/or nuts will have holes drilled through the heads or flats. Safety wire can then be passed through, twisted and attached to neighboring fasteners to prevent rotational loosening.

safety wire







Questions? Want to learn more about locking fastener applications? Contact us at

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Doug Jones
Applications Engineer

December 14, 2018
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Locking Fastener Methods to Secure Your Application: Lock Nuts

Locking part 4

Part four of our series on fastener locking methods will delve into lock nuts, also referred to as prevailing torque nuts because they are not “free spinning” but require a prevailing torque to assemble them.

Many different styles of locking nuts have been developed over the years, but we will focus on two general categories: all metal lock nuts and nylon insert lock nuts.

All Metal Lock Nuts

All metal lock nuts start their life as free spinning nuts but pass through either a press or punch machine which deforms part of the thread to create friction during assembly. Classified as either top lock or side lock, it is a good idea to know the difference and determine the best style for your application.

Top Lock

Top lock nuts have a thread deformation at one end of the nut, meaning assembly can only take place in one direction. The most common type of top lock nut (often referred to as a stover lock nut) has a cone shape on top, making it easy to identify the top of the nut for directional assembly.

stover lock nut






Side Lock

Two-way lock nuts may be assembled in either direction, which allows them to be used in automated assembly. These nuts can be identified by the punch marks on the flats. It is common to have either one punch mark, or two punch marks on opposing flats.

two way lock nut




Nylon Insert Nuts

Nylon insert nuts use a non-threaded nylon ring which gets crimped into the top of the nut at the end of the manufacturing process. As the nut is assembled onto a bolt, threads form into the nylon ring at the top of the nut, creating resistance.

nylon insert nuts





Each style of nut has its advantages and disadvantages. All metal lock nuts can be used at higher temperatures than nylon insert nuts, but nylon insert nuts tend to have more consistent clamp load from lot to lot. All metal lock nuts typically require a wax on top of the normal zinc plated finish to keep from galling, which can result in some unpredictable clamp loads in critical joints.


For more information on locking nuts, check out or contact us at

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Doug Jones
Applications Engineer

December 07, 2018
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Locking Fastener Methods to Secure Your Application: Adhesives

Locking part 2

For part two of our series on fastener locking methods, the focus will be on adhesives. In general, there are two ways to apply locking adhesives to a fastener joint. Liquid adhesive such as Loctite® can be applied to the threads at the time of assembly, or an adhesive patch can be pre-applied to the threads at the time of processing, prior to shipping to the customer.

Liquid Adhesives

The application of liquid adhesives can be done with a squeeze bottle, with a brush, or even rubbed on the threads with a glue stick applicator. One of the challenges with these types of application is getting the right amount on the threads to create the desired locking effect without wasting material. Some manufacturers of liquid thread locker have even developed precise metering guns to deliver the same amount of material for each application.

Liquid adhesives














Manufacturers of thread locking material will give recommendations on how much material and which delivery system makes the most sense for your application, but how does thread locking adhesive work?

The common thinking is that thread locking adhesives simply act as a glue, bonding the male and female threads together so that they cannot rotate loose. Although this is true to some extent, the real benefit to locking adhesives is that they harden after assembly and fill any gaps between the threads. Rotational loosening occurs whenever outside forces (such as vibration) acting on the joint cause a loss of friction in the threads and bearing surface. If the force and the frequency are high enough, air gaps in the threads allow for the loss of friction. Eliminating the air gaps with thread locking adhesive is a very effective way to prevent rotational loosening.

Pre-Applied Adhesives

Pre-applied adhesives prevent rotational loosening in the same manner as described above, but they are applied at the manufacturer as a patch. The adhesive material is microencapsulated so that it will not dry until the fasteners are assembled, crushing the microcapsules and releasing the curing agent.

Some advantages of pre-applied adhesives include:

  • No waste from over-application
  • Adhesive is in the same location each time
  • Cannot be forgotten by the assembler
  • No mess

pre-applied adhesives





A disadvantage of pre-applied adhesives is that they have a limited shelf life which needs to be monitored. If parts have been sitting for too long before assembly, the patch material may dry out and be less effective. Most pre-applied adhesives have a shelf life of 1 – 4 years.

Shop Tape Adhesives

For more information on which thread locking adhesive is right for your application, visit us at or contact us at

Doug Jones
Applications Engineer

November 23, 2018
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Locking Fastener Methods to Secure Your Application: Lock Washers

Locking part 1

This is the first of a five-part series about locking methods for fasteners – the first product we discuss is lock washers.

For joints subject to vibration and cyclical loading, maintaining clamp load and/or keeping the joint tight is one of the biggest fastener problems engineers face. As stated in previous blogs, the best joint design to ensure against loosening is a hard joint with a clamping range of five times the screw diameter, tightened to proper clamp load. When this is not feasible, using a locking fastener method is necessary.

First, let’s look at locking washers:

1. Split Lock Washers/Helical Lock Washers





Available at every hardware store for pennies a pound, these washers have a very limited usefulness as a locking fastener, especially with grade 5 or 8 fasteners (metric property class 8.8 or 10.9). Made of very hard spring steel with a small bearing surface area, the spring rate they produce (the amount of force to flatten) is far below the optimal clamp force of a grade 5 or higher bolted joint. This washer’s use should be limited to grade 2 fasteners, small machine screws or metric property class 5.8 and lower.

2. Ribbed Lock Washers

Ribbed lock washers Ribbed lock washer 2







These conical washers are made to work with higher strength fasteners. The first washer pictured has ribs on the convex side which creates friction between the bearing surface of the fastener (nut or bolt) and works well with grade 5 (metric 8.8) fasteners, but not grade 8 (metric 10.9). The higher strength fasteners have a higher surface hardness, and the ribs will not engage with the bearing surface, limiting their locking ability.

The second ribbed washer pictured above works well with grade 8 (metric 10.9) fasteners. The more aggressive, higher hardness ribs on both surfaces will engage with the harder material to create friction locking.

3. Wedge Ramp Locking Washers

Wedge ramp locking washers







This style of locking washer comes as a pair of washers glued together. The outer surfaces have ribs which are hard enough to work with grade 8 (metric 10.9) fasteners. The wedge ramps between the two washers lock together during tightening, but when loosening the joint, the washers rotate against one another, creating slightly more clamp load as they overcome the angle of the ramp.

It is important to note that any of these locking washers should NOT be used with flat washers, and if used with a bolt and nut joint, they should be on both ends. Rotational loosening caused by vibration will occur at the bearing surface with the least amount of friction, so flat washers should be avoided.

It’s also important to note that because these washers increase bearing friction, more torque may be needed to achieve your desired clamp load. Some washer manufacturers publish recommended torque values, but for critical joints, a joint study is recommended to arrive at your optimal setting torque.


There are many other styles of locking washers, but the ones above will get you through most situations. For more information on locking fasteners, visit us at or email us at

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Doug Jones
Applications Engineer

November 16, 2018
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How to Use Dowel Pins to Reduce Weight

Dowel Pins

Dowel pins are great for aligning, but in a world where light weighting is becoming more and more pivotal, there may be some alternatives to the standard hardened and ground dowel pin.

The first option to review is if a fully ground and hardened dowel pin is necessary. Can a similar result be achieved with a pin that does not require as much processing and hole preparation?

Looking at a simpler way to align mating components may not only be a way to reduce weight in the completed assembly, but also a way to reduce total cost. The alternative to a reamed hole with a dowel pin is to use a counter bored hole with a hollow dowel pin which a bolt or screw can pass through. This is a very effective way to combine functions of the drilled hole required for the dowel pin and the fastener required for clamping the parts together.

Hollow Dowel Pins & Split Dowel Pins

Hollow dowel pins work for many applications and have some benefits associated with them. They can be used to reduce the tolerance required on the mating hole as well as reduce overall weight. Hollow dowel pins can also come with a split in them. This split offers some advantages over seamless hollow dowel pins. Split dowel pins are easier to manufacture than seamless hollow dowels and can be used with a tolerance zone that isn’t as tight as standard dowel pins.

Another great alternative for plastic parts is barbed pins. These allow the material flow around the barbs to lock in place. If a pin needs to be locked into metal, this can be done with a knurled pin or a grooved pin. Both of these pins can act as a pivot and can also be used for locating purposes.

For more information about dowel pins and how they can be used in your application, contact us at

Brandon Bouska
Application Engineer

October 05, 2018
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4 Handy Tips from an Engineer for Using Washers

Washer Selection

When designing joints with washers, it is important to understand and use the correct washer for the job. Below are a few tips for making a good selection:

1. When using flat washers, match washer hardness with bolt and/or nut hardness to avoid joint settling.

  • 140 HV ≤ 8
  • 200 HV ≤ 8
  • 300 HV ≤ 9

2. Split lock washers are not intended for use with hardened bolts/nuts, only with property class ≤ 8.

Washer 1

3. Toothed lock washers are designed to permit electric current flow between components, and do not provide much of a locking feature. They are also only used for low property class ≤ 8.

Washer 2

4. Specialty washers exist for high strength joints, for example:

  • Rip-Lok – designed for property class 8.8
  • Conical spring washer with serrations on top

Washer 3

  • Schnorr washer – designed for property class 10.9
  • Small OD conical spring washer with serrations on both sides

Washer 4

For more details on selecting the correct washers for your application, checkout or send us an email at

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Doug Jones
Applications Engineer

September 28, 2018
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Quick Guide: Installing Rivet Nuts

Rivet Nuts

How do I know if I have the right installation force? Did I set it right? Do I have the right tool? These are some of the most valid questions when installing and using rivet nuts. Knowing the mating material, grip range, hole size, and clamp force will aid in getting the right fit for the joint in your application. Securing a proper clamp load will prevent from loosening and/or rotational loss. Understanding the creep and material relaxation is also important when using this joint design.

Finding the Correct Fit



Examples of Rivet Nut Applications

There is a lot to consider when choosing the right rivet nut. There are many choices for body styles, material, and coating finishes. Let the experts at Bossard help you narrow down your search and get you on the right path to a secure joint. Let us help you save money and avoid costly warranties or claims. Contact us at to learn more.

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John Syharath
Technical Sales

September 14, 2018
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How Pre-Applied Thread Lock Patches Can Save You Time and Money

Preapplied Thread Patches

If assembly requires applying liquid thread locker to any threads, pre-applied thread locking patches should be investigated.  Pre-applied thread locking patches could potentially be an untapped area for both time savings and cost savings.

Thread Locking Materials

Pre-applied thread locking materials work in a couple different ways. A nylon thread locker pushes work by forcing metal to metal contact between the threads on the opposite side of the applied area. Because of the way this type of thread locker works, coating all 360° of the threads is not advised.  This type of patch can be reused if care is taken. A thread locking patch works like a two-part epoxy. When installation occurs, the two parts mix together and after the two parts set, the area between the threads are filled. This type of thread locker can only be used once and if the joint needs to be serviced, a bolt with a new patch must be used.

Filling the thread tolerance area between the threads will help resolve some vibrational loosening that might be occurring.

There are many features of pre-applied thread locking patches including the amount of locking material applied to the threads is more consistent, parts can be processed in large lot quantities, and the pre-applied thread locking patch usually has a long shelf life.

Please feel free to contact Bossard to help answer any questions that may arise.

For more information on thread locking patches, check out or contact us directly at

Brandon Bouska
Application Engineer

September 07, 2018
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Benefits of Low Force Seals

SFC Koenig Banner

Now more than ever consumers are demanding vehicles that are ecologically friendly, as well as fuel efficient, so they can save more at the pump. To meet this demand, automotive engineers are faced with the task of designing capable engines to fit these new requirements. Often, that means making the engines on all vehicles, from small compact cars to large trucks, smaller and lighter.

To reduce engine weight and size, the components must be tightly condensed together, giving the engine parts little wiggle room. The necessary ports and passages used to deliver oil and all the other mandatory engine operations must be carefully integrated into the remaining available space, resulting in thin port walls.

The Challenge of Thin Port Walls

Engine Block BossThin port walls are quickly becoming more common, but they aren’t built to withstand the usual methods of older style plugs, such as cup plugs or threaded screws. These older plug styles can vary greatly in their results, causing a larger fluctuation in process performance—and with thin port walls and tightly packed engine components, even a small discrepancy during the installation process can cause a disaster.

The process must be precise and accurate every time to prevent damage or leakage, as many times ports are in a dangerous proximity to bearings or moving parts. Engineers have consequently been relying on low stress expander seals to attain reliable, precision sealing.

Benefits of Low Force Seals

Low Force SealsLow force seals, such as SFC KOENIG EXPANDER® plugs, cause less damage to the port wall and components, having minimal effect on even the most complex engine geometries. All the advantages of low force seals are listed here below:

  • Less negative effects on engine components
  • Prevent cracking of base
  • Avoid expansion of port into nearby components
  • Reduce the risk of leaks and wear
  • Less effect on overall system performance
  • Comes with its own installation equipment to ensure needed precision; gives the installer more control

Unlike cup plugs, threaded plugs and the like, low force seals provide leak-proof security and work well when dealing with extremely sensitive applications. Their reliability is even more critical when dealing with ports located deep within the maze of a tightly packed engine. Due to the little to no margin-for-error in engines with thin port walls, the strict tolerances and reliable installation methods of low force seals are essential to the successful performance of these modern machines.

For more information about SFC KOENIG EXPANDER® plugs and their other products, contact us at

August 31, 2018
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A Complete Guide to Fastener Strategy – Part 4

Fastener Strategy Part 4

Another consideration when building a fastener strategy is drive styles, especially in smaller screws with internal recess drives. If no fastener strategy is enforced, many customers may have several different styles in their bill of materials, creating a proliferation of similar parts. Some of the more common drive styles are shown below:



  • A slotted head style is not recommended for use in high volume or automated assembly. Sometimes this drive is still the best option for access panels that need to be serviced in the field using simple, readily available tools.


  • This is a common drive for most head styles and okay for higher volume assembly. One disadvantage is that the tapered side walls of the drive require significant down force during tightening or removal to prevent the tool from slipping and damaging the drive. Once the drive is damaged, it can be hard to remove.


  • Similar to Phillips, a Pozidriv head style has vertical side walls in the drive which have less tendency to “cam-out” when installing or removing. This drive typically extends tool life in high volume assembly but does require a Pozidriv driver bit which can be confused for a Phillips drive bit. Pozidriv heads can be identified by the four tick marks around the cross (see above). Driver bits are marked with a “pz” while Phillips are marked with a “ph”. 

Torx, Torx Plus or Hexalobular

  • These drives have been around for several years and are more readily available in metric than inch hardware. Torx and hexalobular are very similar and use the same driver, while Torx Plus has slightly different geometry and offers longer tooling life in high volume assembly. Torx driver bits are marked with “T” while Torx plus are marked with “IP”.


  • This is an internal hex drive which uses a hex key, sometimes also referred to as an Allen key. It is often used in larger diameter bolts which have limited space for a standard socket as a driver. In smaller screws, the internal hex may become damaged as tooling wears, which can make them difficult to remove.

For more information on the availability of these drive styles, and which one best fits your needs, check out or contact us directly at

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Doug Jones
Applications Engineer

August 24, 2018
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