A sling is a system, and the rope is one part of it

A rope plus terminations at both ends, hooks, shackles and a master link makes a sling. The rated load belongs to the whole assembly, not to the rope breaking force: the number on the tag already includes termination efficiency and the reduction for the hitch.

So the same rope has different ratings as a single-leg and as a choker sling; and even with the same hitch, a change in sling angle means the load must be recalculated.

Single leg: the simplest, and the easiest to overrate

A single-leg sling is the simplest form: one end on the hook or master link, the other on the load. In a vertical lift the single-leg rating is the figure on the tag, and other hitches are derated from it.

Once the leg is inclined, the tension in the rope exceeds the weight of the load. The further the rope leans from vertical, the higher the tension; this is the same geometry as multi-leg slings, but it is easier to overlook on a single leg.

Single legs suit a clear centre of gravity, a single attachment point, or topping up a multi-leg assembly. Two single legs used independently cannot simply be added together as a multi-leg sling.

Choker: convenient, but derated

A choker passes the rope around the load and through the loop formed at the other end, drawing tight around the load. It needs no lifting eye and suits items without attachment points, but the rating must be reduced for the choke.

The usual factor is about 0.8, so a choked sling is roughly 80% of the vertical single-leg rating, subject to the standard and the sling maker's data. The reduction exists because the rope bears on itself at the choke, adding bending and squeezing.

Choke angle also matters: the closer the choke leg is to square with the load surface, the tighter it holds; at a slant the rope may slide along the item. Sharp edges need protectors first, or the outer wires at the choke break first.

Basket: two legs share, and the angle decides everything

A basket sling passes the rope under the load and hooks both ends on the hook, creating two load-bearing parts. If both parts are vertical, basket capacity is about twice the single-leg rating.

As the angle between the parts opens, tension in each part rises and the basket advantage falls. At 120 degrees between the parts, each part already carries the full load.

A basket needs a hook wide enough for both parts, and the parts must not rub on each other. With sharp edges under the load, protectors are essential, because the basket contact is at the bottom of the load where pressure concentrates.

Sling angle: the factor shared by every type

Sling angle usually means the angle between the two legs, or between one leg and vertical. The wider the angle, the higher the rope tension; this is geometry, not rope quality. State which definition is being used, or the same 45 degrees can describe two completely different geometries.

A practical estimate is to take the vertical component and divide by the cosine of the angle. At 60 degrees between legs each leg carries about 0.58 of the load, at 90 degrees about 0.71, and at 120 degrees each leg carries the whole load. For the relationship between angle and load, see sling angle and load

The most useful site rule is to keep sling angle within 60 degrees and to state the angle basis on the sling tag. Beyond 60 degrees, use longer slings or a larger rope.

Multi-leg: never assume every leg shares equally

Load sharing in three-leg and four-leg slings depends on the centre of gravity, the attachment layout and the length of each leg. Whichever side the centre of gravity favours carries more load.

Standards usually derate by leg count: a four-leg sling may be rated as three-leg or even two-leg, and a three-leg as two-leg, according to the standard applied. The rule exists because equal sharing is hard to achieve in practice. When the attachment points are not in one plane, sharing becomes even less certain and the working load should be reduced.

Adjust leg lengths so the load hangs level and no leg goes slack while the others overload. The master link and hook must be rated above the sum of the leg loads.

End fittings, edge protection and tags

Sling ends commonly use hooks, shackles, master links and thimbles. Hooks should have a latch, shackles must match the sling rating, thimbles protect the eyes and edge protectors keep the rope from being cut on sharp corners.

Every sling should carry a tag stating rated load, length, type, date of manufacture and serial number. The tag is the sling's identity; without it the rating cannot be confirmed and the sling should be taken out of service.

Edge protection is not an optional accessory. A sling without protectors can suffer broken wires on a sharp edge in a single lift, and those breaks are inside the sling where they may not be visible.

Selection order: start with load and centre of gravity

First establish the weight and the centre of gravity; second fix the number and position of attachment points; third choose the hitch: single leg, choker, basket or multi-leg.

Fourth calculate the sling angle and the load per leg and select rope diameter and terminations; fifth specify end fittings and protectors; sixth check safety factor and standard requirements. For how the safety factor is set, see the wire rope safety factor guide

If the load has sharp edges, heat or corrosion, add protectors, insulation and material requirements to the selection. A sling rating is established under stated conditions, and changed conditions require a new calculation.

• Confirm load weight and centre of gravity, not an estimate.
• Confirm attachment point positions and capacity.
• Confirm sling angle stays within 60 degrees.
• Confirm protectors, tags and inspection records are in place.

Inspection and discard

Sling inspection focuses on terminations, choke points and attachment points. At terminations look for broken wires, corrosion and deformation; at choke points look for crushed outer wires; at attachment points look for wear on thimbles and hooks.

Broken wires, reduced diameter, kinks, bird-caging and cracked terminations are all discard signals. A sling that has taken a shock load or an overload should be further inspected or downgraded even if it looks normal.

Sling discard is stricter than rope discard because slings are rigged and re-rigged and see loads from changing directions. For the basis, see the wire rope discard criteria

To have slings made up for specific attachment points, angles and loads, state the duty in one go through the wire rope quotation page