Shackles may look easy enough: a U shaped steel piece with a pin to cover the opening. That, however, may be misleading. Shackles do not look simple. Shackles may fail if misused, and the results can be catastrophic.
Some shackles may have their working load limit marked. If the load falls within this limit, the load limit may be misleading. Shackles may be rated by their lifting capacity, but ultimately they are rated by their utilization. Some examples may be classified as a screw pin against the application, a D shackle when a bow shackle is required, and side loading where the hardware is designed for side-loading. These shackles may all be calling for a disaster.
Shackles are the hardware that connects your load to your sling. If you select the proper hardware then the lifting capacity is proper. If not then you may be risking the most loaded part of your entire rig.
Bow or D — which matters.
The two types of shackles are bow shackles, at times called anchor shackles, and D shackles, chain shackles. Although they are both of a similar design, and are capable of lifting similar loads, they are not interchangeable.
Bow shackles have a wider and more rounded design. This design allows for multiple sling legs to be hooked to the shackle while the load is not in a direct line, as they may pull at an angle. This design is required when a load is hooked to a multi-leg bridle where the load is not in line with the connection point of the bridle.
D Shackles are narrower and made for straight line pulls. They typically have one chain, one sling eye, and the load is applied directly through the center. If you try to fit two sling eyes side by side in a D shackle, they will rock from side to side when under load. This will place bending stress on the body and the fittings that the rated capacity will not account for.
If a D shackle is used in place of a bow shackle, capacity is not the only loss – a failure is introduced that also was not accounted for in the design.
## Screw pin or bolt type – and when it becomes critical
The pin is how you close the shackle. There are two common types.
Screw pin shackles have a threaded pin that screws into the body. They are also designed to be fast for pick and place work because of how quickly they close and open. This is great for work in the field that requires frequent rigging and de rigging. Loading that creates a vibratory motion where the load is under a shackle in a D design also creates a loss of capacity and strap integrity if the strap loosens.
Bolt type shackles are another closure design. They have a bolt and split pin. This creates a loss capacity under a significant load designed to provide safety enforced under a shackle closing. These loss of safety factors are also designed for load that is to remain permanent and not of a type to support a load that is under a shackle in a D design.
If you’re using static loads and you’re unhooking at the end of the shift, then screw pin is fine. In other situations, use a bolt type.
Side loading reduces capacity – or breaks the shackle
Shackles are designed to work with an in-line load. In-line load means the pull will run in a straight line through the body of the shackle, from the bow to the pin. It is not designed to work with a sideways load.
Side loading can greatly reduce a shackle’s working load limit, generally, by half or worse. Some shackles can be used with a side load, but you must derate it according to the chart from the manufacturer. However, D shackles generally can not.
If side loads are generated by your setup, then you must use a different connection method or a swivel instead. It is incorrect to expect your connection to break before the shackle breaks.
The tag is not optional
The standard establishes that every shackle should exhibit the working load limit, the manufacturer’s mark, and the material grade on the shackle itself. If, for some reason, those marks are illegible or absent, the shackle is no longer used. It is not accepted as “probably still good”.
Without a legible tag, you’re guessing the capacity. And if you guess wrong, people get hurt.
Never swap pins between shackles
If a pin goes missing, the shackle gets binned. You don’t replace it with a bolt from the van or a pin from another shackle.
Shackle pins require better materials and heat treatment to be able to handle the loads. Things like random bolts do not. They may look the same, but they will not handle the loads. Using makeshift fasteners in rigging is directly against HSE.
Pre-Checks That Matter
Someone checks the shackle before every single lift. Not just a quick glance, they actually inspect it.
Look for bent or stretched body, damaged threads, worn or corroded pins, pin damage, missing pins, cracks/gouges, no markings or illegible markings.
If the body is the slightly elongated or the U shape is slightly stretched, it is scrap. If the pin threads do not screw in or seat and screw properly, it is scrap. If there is a doubt, do not use.
Why It Matters
Shackles need to be matched to the job. This means needing the right type, right pin, right capacity, and right condition. If you miss one of these, you have a weak point.
LOLER regulations will cover shackles the same way covering slings. It will cover regular inspections, right record keeping, and classing. HSE will expect you to know and should not ‘look’ right.
Need Lifting Gear Training? ACT Construction Training offers LOLER courses for shackles, slings, and rigging hardware through various approved local training providers. Please contact us via email with any inquiries at info@act-constructiontraining.co.uk