The first and most obvious thing a rigger considers when selecting below-thehook equipment is the shape of the item to be lifted. Geometry sets the stage for everything that follows. Upon visual assessment, it is usually clear whether a lifting sling, clamp or a combination will be required to move the load safely. Yet this seemingly straightforward choice leads to a range of further considerations that can separate a safe, efficient lift from one that risks equipment, product or people.
If a solid, round bar is the object in question, a lifting clamp offers no realistic option, and a sling is the obvious choice. Conversely, when handling a large steel plate, a sling may be as redundant as a clamp would be in the first example. But rigging is rarely that black and white. As soon as more than one clamp is required, for instance, a sling may be introduced to connect them back to the crane hook or a central lifting ring. In this way, slings and clamps are often not alternatives, but companions in the same rigging arrangement.
The presence – or absence – of lifting points can also steer a rigger towards slings. While purpose-designed lifting lugs are sometimes engineered into equipment, raw materials such as steel stock, timber beams and pre-cast concrete panels usually do not include them. Even when lifting points do exist, a competent rigger must verify that they are designed for the whole load, not just part of it. A small eyebolt, for example, may be intended for handling a motor during maintenance, not for lifting the entire machine in which it sits. Misinterpreting such points is a mistake that can lead to load imbalance or failure.
When two lifting points are available, the line between them must pass directly through the centre of gravity, or instability will follow. With three points, the centre of gravity must lie within the triangle they create. Four points add further complexity, as the load must be evenly shared by all legs – easier said than done in practice. A rigger’s understanding of geometry and balance is, therefore, as important as the hardware itself.
Where no lifting points are available, ingenuity and experience come into play. A sling may be attached through a threaded hole with a suitable eyebolt, or it may pass through an aperture in the load. Passing through has the advantage of making the load captive. Wrapping a sling around a load is another common technique, but it requires careful planning to ensure it cannot slip free during the lift. In all cases, protection of both the sling and the load is essential; edges must be padded, and care must be taken not to score or crush the product.
Another versatile option
Clamps provide a versatile option, and their design is sometimes misunderstood. By their nature, clamps generate a perpendicular clamping force, either through geometry – where the pulling action tightens the grip – or by tightening a screw. This principle makes them useful not only for attaching a load to a hoist, but also for anchoring, pulling or positioning. The key limitation is that the load itself must be strong enough to withstand the squeezing force applied by the clamp. Not every material, surface or component is suitable.
Specialised clamps extend these principles to more challenging shapes. In many manufacturing environments, pipework or curved plate must be handled. Standard vertical clamps would struggle, but purpose-designed products make such lifts possible. One example is Caldwell’s turning, locking, curved-surface clamp, sometimes called a TLC clamp. This tool incorporates a ‘lock open’ and ‘lock closed’ feature to simplify attachment and removal, while a specially engineered cam jaw grips both curved and flat plate securely. Designed with pipe lifting in mind, these clamps are also suitable for any load that meets their minimum radius specification.
The broader lesson is that there is rarely a onesize- fits-all solution below-the-hook. Every lift has its nuances, from geometry and centre of gravity to surface condition and load fragility. A rigger’s role is not just to attach hardware, but to make a series of informed decisions that determine whether a lift is safe, efficient and productive. That judgment grows with experience, but it must always be supported by training, inspection of equipment and respect for the fundamental principles of rigging.
As the industry continues to innovate, with new clamp designs, stronger synthetic sling materials and modular lifting accessories, the range of options available to riggers will only increase. But the underlying questions remain timeless: what is the shape of the load? Where is the centre of gravity? And which combination of tools will control it best? By keeping those fundamentals in mind, riggers ensure that what happens under the hook supports – not undermines – the lifting technologies above it.
