Shackles are the connector of choice for many slackline applications. They are strong, reliable, predictable and made from steel. There are three common shackle shapes: bow, dee (D) and twist shackles. Bow shackles are designed to be tri-loaded and take the loading better than any other type of connector commonly used in slacklining. Dee and twist shackles are intended for straight loading and have more limited applications. Shackles also contain different styles of pins.
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Shackles have a broad range of application, so it is important to be aware of the quality of the shackle that you are purchasing. Sailing stores, hardware stores, the rigging and lifting industry, and slackline specific shops are all locations that sell shackles. The trouble with shackles is that they do not always have a rating stamped on the body and they are not always made from the same type or quality of steel. What you typically want to look for is information on the WLL. Some shackles have it stamped on the body, while others, especially in sailing stores, do not. There you might have to ask the seller for the load specs. Employees in hardware stores usually are not very helpful because they generally do not need to know this information for typical shackle applications, and slacklining is anything but typical!
The SF on shackles is usually 5:1. This means, if you buy a shackle that says 1t (ton), or “WLL 1t”, on it, then you have a MBS of 5t. Always determine if the shackle is suitable for the load it will carry. The only major downside shackles have is that it’s possible to lose the pin and they can magically unscrew when not under load. So always be sure to check your pins before you apply load to your system. If unscrewing is an issue, use and properly close safety bolt shackles, which are much less likely to unscrew.
If you ever have a really hard time opening a shackle after use, chances are you may have gone over WLL and deformed the material. If this is the case, it is best to retire the shackle. Bent shackles can sometimes still be opened with some elbow grease to remove equipment. If it sticks at the start then unscrews easily then your shackle might just giving you some attitude.