All About Shackles

Shackle - A U-shaped piece of metal that is secured by a clevis pin or bolt and nut across the opening.

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Shackles are used for all kinds of different applications, from industrial rigging to sailing. Any time an extremely strong and reliable connection point is needed, usually a shackle suits the application best.

We use shackles for slackline rigging all the time, but not all shackles are built the same. Even among the different varieties of shackles there is quite a bit of variation. There are, however, a few characteristics that not all shackles have that are absolutely necessary for our application.

One trait that is necessary for a shackle to have for it to be acceptable for use in slacklining is either a fixed working load limit or known breaking strength. Some shackles are not built to withstand sustained loads and this is very dangerous in slacklining. We typically see loads in the 1,000 - 5,000 lbf range and to have a piece of metal explode with this much energy behind it can be extremely damaging and even fatal. So, for this reason, only use shackles that either have a working load limit stamped on the shackle, or a reliable breaking strength displayed on the retailers website.

Another feature that's absolutely necessary, especially for anchor shackles, is reliability. As I mentioned above, not all types of shackles are made the same. Even shackles that have a stamped working load limit can be unreliable. I went to a local wire-rope shop that has a giant pull testing machine to do some break tests recently and I was talking to the owner of the shop. He said that one time he was testing a batch of 3/4" Anchor Shackles that came from China. These shackles all had a working load limit of 7-tons stamped on the body. He pulled all of these shackles to the point of failure and all of them tested out above the specification except for one. This one shackle broke at a measly 3,000 lbf, or 1/5 of the working load limit, which is supposed to have at least a 5:1 safety ratio! This goes to show that manufacturer errors DO happen and for a piece of gear that we put so much faith into, we need be absolutely sure it is reliable. The only way to do this is to only purchase shackles that are individually tested for strength, or at the very least, batch tested. Companies such as Van Beest, Crosby, and CM test a set percentage of the shackles they produce to be sure the entire batch is reliable and consistent. Other companies, such as Peterson, pull every single one of their shackles to 2x the working load limit to be absolutely sure that it will withstand the loads that they advertise them to. These shackles may cost a few extra dollars, but they are guaranteed to hold the working load limit for as long as they are used.

Last but not least, something that you should pay attention to is how a given shackle is manufactured. There are typically two ways a shackle is made: forging and casting. Forged shackles are made by taking a plate of steel and smashing down on it with a large hammer that has a shape cut out on it; this shape imprints on to the plate of steel. This method ensures that the entire shackle is of the same grade and density of steel. Cast shackles are made by pouring molten metal into a mold and then allowing it to dry. This process allows for air bubbles to form and persist within the finished item, which can severely decrease the breaking strength. For this reason, cast shackles are usually not rated for lifting and typically do not have an advertised breaking strength or working load limit.

With these attributes in mind, let's take a look at the different kinds of shackles.

Anchor Shackle

Often referred to as bow shackles (although, they are NOT the same as the bow shackles below), these are most commonly used for industrial applications. They are typically forged from galvanized steel and the ones made for lifting are stamped with a working load limit (WLL). For each size of shackle, there is usually a standard working load limit (i.e. 1/2" shackles usually have a 2-ton working load limit). However, this is not regulated, so there are some non-standard shackles out there that have higher or lower working load limits than others. Be sure to only use shackles that are rated for lifting and are tested for reliability.

In slacklining, Anchor shackles are great for your anchors. There shape is ideal for situations where there are more than 2 directions of loads (i.e. at the anchor). Because of this, we can use shackles even in situations where we have many many directions of loads, like on a highline anchor with lots of bolts. However, the working load limit on shackles should be reduced by a small amount, depending on the angles the load creates at the shackle (as described in this article: http://www.vanbeest.nl/public/files/catalogue/en/Chapter01_Shackles.pdf).

Anchor shackles are the most common shackles out there. Because of this, their dimensions are pretty standard. It's important to know what the dimensions of your shackle are before purchase because certain applications require certain sized shackles. Please refer to the image below to find the most common dimensions of the popular Anchor Shackle.

Bow Shackles

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Bow shackles are very similar to anchor shackles in their shape, but the actual 'Bow' of the shackle is far bigger than an anchor shackle. These types of shackles are most commonly made of stainless steel or titanium and are very nicely suited for slacklining due to their geometry. The 1/2" (12mm) size usually has a 1" width at the mouth, which makes it perfect for a webbing anchor.

Be careful with Bow Shackles though, as they are the most common shackle that is made from cast stainless steel. Be sure to look for the forged variations of them for the highest reliability.

Because bow shackles are so common, the dimensions are fairly consistent. Here is a chart that shows the dimensions of some common sized bow shackles:

Chain / Dee Shackles

Chain shackles, also referred to as Dee Shackles, are straight-legged shackles that are typically used in bi-directional load situations. Their shape is optimized for two directions of pull, which makes them great for connecting pieces of gear together (such as your pulleys to the rigging plate, or your rope to the becket of your pulleys). These types of shackles are not good for situations where there are more than two directions of loads because of their geometry. The angled loads place a great deal of stress on the bolt-side of the shackle and can cause premature failure.

Be careful when purchasing Chain Shackles. Although they are often referred to as Dee Shackles, they are not always the same as Dee Shackles. The geometry of the two is slightly different and they are often made from different materials. Here are images of the dimensions of both types of shackles:

Twist Shackles

Twist shackles are very similar to Dee Shackles, but they are twisted 90-degrees. These are great for when you need to rotate gear and you don't want to use two connectors. Although, it's hard to find twist shackles that are large enough to hold the full force of your line, the small ones are great for connecting components together in your pulley system (i.e. for rotating your brake 90-degrees so that the handle is facing downwards).

There are hundreds of other types of shackles out there and they all serve a purpose. The shackles above are the most commonly used in rigging and slackline applications.

Let us begin with shackles. The most common style of shackle you see on the trails is the bow shackle. They are an essential piece of hardware for you to have in your recovery kit.
They come in a variety of sizes to suit various application. Here is an example of that. Starting with a 1/8" 500lbs WLL on the left and finishing with a 2" 35ton WLL on the right.

The right shackle for the job, WLL (working load limit) and getting what you pay for. For the most part we in the overlanding community tend to have some really heavy rigs. I have seen individuals on the trails that have either damaged there equipment or have gotten injured from using a shackle that wasn't rated for the load it was carrying or it had no working load limit at all. There are some shackles available on the market that are genuinely just to be used to look at. Those would be any shackle that does not have a WLL stamped into them! What am I saying?
If there is not a load limit on the shackle it should never be used in any capacity other than a paper weight. Basically don't use a cheap knockoff shackle your life could depend on it. Know what your shackles are rated for and use the correct size for the task at hand.

Where is the WLL?
It is typically stamped into the fording. Example.

Bow shackle working range. Yes they have one. Most shackles have the working angle stamped into them just like the WLL. To many times I have seen people trying to pull a rig side ways on a trail and they have the shackle seriously side loaded. Bow shackles have a very wide working angle on the PIN on its normal rotating plane. As long as the shackle is free to move and not binding on any other object it is good. Where you run into issues is with the BOW. The bow is limited to a 90* working angle. Anything beyond that can cause irreparable damage to your shackle. Example of Working angle pictured below. You can see the "45" with the line above it on both sides of the bow.

Inspecting your equipment. Always inspect your rigging before each trip and before and after each use.
With your straps check them end to end for tears, abrasions, UV damage, burns, petroleum contamination, broken/unraveled stitches and make sure the capacity tag is intact/legible. If you find any issues destroy and discard of the strap properly. (Cut the eyes on each end and put it in the plastics recycling bin.)

With shackles you should always check them for deformation, cracks, excessive wear and legible WLL stamps. Shackles should not be painted or powder coated unless it was done by the manufacturer. Doing so prevents proper inspection.
Easy way to check for deformation is to look at the pin when it is fully threaded into the bow. It should be seated against the bow at the head and the threaded end should be flush or just protruding past the bow. If it is not flush on either end it is bent and unserviceable. Destroy and dispose of properly.

Shackle on the left is in good shape shackle on the right is deformed and unserviceable.

Example of excessive wear and damaged WLL markings. Unserviceable.

Nesting straps in a shackle correctly is also important in preventing damage and failure.
Over filling or using to small of a shackle can cause the shackle to cut the strap or cause the straps to friction bond to each other. Having the shackle in the wrong orientation can cause deformation and failure of the shackle.
Examples of improper nesting of a bow shackle.
Bow is side loaded, this will damage shackle. Solution is to turn the shackle 90* so that the strap rides on the pin and the arc of the bow.
Pin throat is to narrow for strap. This will cut the strap and possibly cause accident/injury. Solution is to use a larger shackle that fits the strap.

Proper shackle nesting and strap joining examples below.
Correctly joining two straps with right size shackle for the strap.
Correct nesting for basketed strap to single strap. Commonly used when using a tree saver connected to a recovery strap. Strap in pin throat could also be substituted for your winch link or hook.

Example of a reef knot. I personally will only use this method in a last resort situation because it to can cause damage to the two straps being joined.

Straps should always be connected with a shackle or with a reef knot. Basketing, tying and daisy chaining them will cause damage and/or failure of the straps. A soft shackle of the appropriate size or a bow shackle should always be used. Connected straps should always be weighted with a line weight or a jacket to reduce recoil in the event of failure. Proper joining techniques covered above. Examples of what not to do below.

Example of a daisy chain. This will lock the straps together and cause them to cut one another.
This is basketing one strap to another. This can also cause failure of the tow straps.


I hope this information helps feel free to comment. If you have any questions please ask I'll do my best to answer and update as necessary.

Over the years I have seen many accidents and injuries as a result of improper rigging with straps and shackles. I thought I would offer up some information on the subject to help the OB community out.Let us begin with shackles. The most common style of shackle you see on the trails is the bow shackle. They are an essential piece of hardware for you to have in your recovery kit.They come in a variety of sizes to suit various application. Here is an example of that. Starting with a 1/8" 500lbs WLL on the left and finishing with a 2" 35ton WLL on the right. The right shackle for the job, WLL (working load limit) and getting what you pay for. For the most part we in the overlanding community tend to have some really heavy rigs. I have seen individuals on the trails that have either damaged there equipment or have gotten injured from using a shackle that wasn't rated for the load it was carrying or it had no working load limit at all. There are some shackles available on the market that are genuinely just to be used to look at. Those would be any shackle that does not have a WLL stamped into them! What am I saying?If there is not a load limit on the shackle it should never be used in any capacity other than a paper weight. Basically don't use a cheap knockoff shackle your life could depend on it. Know what your shackles are rated for and use the correct size for the task at hand.Where is the WLL?It is typically stamped into the fording. Example. Bow shackle working range. Yes they have one. Most shackles have the working angle stamped into them just like the WLL. To many times I have seen people trying to pull a rig side ways on a trail and they have the shackle seriously side loaded. Bow shackles have a very wide working angle on the PIN on its normal rotating plane. As long as the shackle is free to move and not binding on any other object it is good. Where you run into issues is with the BOW. The bow is limited to a 90* working angle. Anything beyond that can cause irreparable damage to your shackle. Example of Working angle pictured below. You can see the "45" with the line above it on both sides of the bow. Inspecting your equipment. Always inspect your rigging before each trip and before and after each use.With your straps check them end to end for tears, abrasions, UV damage, burns, petroleum contamination, broken/unraveled stitches and make sure the capacity tag is intact/legible. If you find any issues destroy and discard of the strap properly. (Cut the eyes on each end and put it in the plastics recycling bin.)With shackles you should always check them for deformation, cracks, excessive wear and legible WLL stamps. Shackles should not be painted or powder coated unless it was done by the manufacturer. Doing so prevents proper inspection.Easy way to check for deformation is to look at the pin when it is fully threaded into the bow. It should be seated against the bow at the head and the threaded end should be flush or just protruding past the bow. If it is not flush on either end it is bent and unserviceable. Destroy and dispose of properly.Shackle on the left is in good shape shackle on the right is deformed and unserviceable. Example of excessive wear and damaged WLL markings. Unserviceable. Nesting straps in a shackle correctly is also important in preventing damage and failure.Over filling or using to small of a shackle can cause the shackle to cut the strap or cause the straps to friction bond to each other. Having the shackle in the wrong orientation can cause deformation and failure of the shackle.Examples of improper nesting of a bow shackle. Bow is side loaded, this will damage shackle. Solution is to turn the shackle 90* so that the strap rides on the pin and the arc of the bow. Pin throat is to narrow for strap. This will cut the strap and possibly cause accident/injury. Solution is to use a larger shackle that fits the strap.Proper shackle nesting and strap joining examples below. Correctly joining two straps with right size shackle for the strap. Correct nesting for basketed strap to single strap. Commonly used when using a tree saver connected to a recovery strap. Strap in pin throat could also be substituted for your winch link or hook.Example of a reef knot. I personally will only use this method in a last resort situation because it to can cause damage to the two straps being joined.Straps should always be connected with a shackle or with a reef knot. Basketing, tying and daisy chaining them will cause damage and/or failure of the straps. A soft shackle of the appropriate size or a bow shackle should always be used. Connected straps should always be weighted with a line weight or a jacket to reduce recoil in the event of failure. Proper joining techniques covered above. Examples of what not to do below.Example of a daisy chain. This will lock the straps together and cause them to cut one another. This is basketing one strap to another. This can also cause failure of the tow straps.I hope this information helps feel free to comment. If you have any questions please ask I'll do my best to answer and update as necessary.

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