Sling Selection Guide

1. Calculate the load first, then talk tonnage

The first step of selection is not the sling — it is the load. Confirm three things: the total weight, the centre of gravity, and the number and position of the lifting points.

With multi-leg lifts, load is not shared equally. The leg on the side the centre of gravity shifts toward carries more. In a symmetric four-point lift, if the CoG is offset, a single leg may carry over 40% of the total. A common conservative rule: split the total weight across two legs for two-leg lifts, and calculate four-leg lifts as if only three legs are loaded — i.e. assume one leg carries nothing and the remaining three share the full weight.

2. Hitch load factors (the core table)

The WLL printed on a sling label is the default for a vertical single-leg lift. Switch to another hitch and you must multiply by the factor below. Actual allowable load = rated WLL × hitch factor.

Note: the included angle is the maximum opening angle between the two legs of the sling. Factors are common industry values; refer to the applicable standard and the product label.

3. Safety factor: how 7:1 (EN) and 5:1 (ASME) come about

The safety factor is the ratio of breaking force to rated load. It is not a margin for "how many times you can overload". It absorbs dynamic shock, repeated bending, edge wear and the uncertainty of on-site misuse.

A 2 t sling made to EN 1492-1 must have a breaking force of at least 14 t; made to ASME B30.9, at least 10 t. That is why products for different export markets must be manufactured to the corresponding standard — one label cannot sell worldwide.

4. Width vs tonnage (reference table)

The capacity of a flat webbing sling mainly depends on webbing width and ply count. The table below shows the common correlation for single-ply, vertical-lift conditions, for initial selection:

Reference values: single-ply webbing, vertical lift. Multi-ply, endless slings and different materials vary; the final WLL is the one stated on the product specification.

Width also depends on the workpiece: a narrow sling concentrates pressure and can mark soft or surface-sensitive loads; a wider sling conforms better but is heavier and costlier. Where edges are sharp, widen or add a sleeve rather than "lifting a little less" to compensate.

5. Material & service conditions: don’t look at tonnage alone

Special conditions add options: fire / heat-resistant sleeves (welding, foundry), acid-wash dedicated (plating, pickling lines), cut-resistant sleeves (steel plate, casting sharp edges). When temperature exceeds the material range, you must derate or switch to a chain sling.

6. Edge protection: the number-one killer of synthetic slings

The typical failure of a synthetic sling is not "breaking" but being cut by a sharp edge. The edges of steel plate, castings and machined parts slice into the webbing like a knife under load — cutting through in seconds.

• Add a sleeve: a polyurethane or high-strength fibre sleeve over the contact point absorbs the cutting force;
• Add a corner protector: a metal or plastic protector under the edge turns line contact into surface contact;
• Increase contact area: choose a wider sling, or pad the lift point with soft material;
• Change the hitch: use a basket instead of a choker to reduce relative sliding against the edge.

7. Colour coding: read the tonnage at a glance

EN 1492-1 mandates a colour code for flat slings; the colour maps directly to the rated load, so you can judge capacity on site without reading the label:

Some products also weave in black stripes — one per ton — as a second quick identifier. Colour coding is a hard requirement for CE-marked products entering the EU market, not decoration.

ASME B30.9 does not mandate colour coding and relies mainly on labels; US-bound products follow ASME label requirements.

8. Retirement criteria: discard on any one of these

A sling is a load-bearing safety component — never "use it a bit longer". Visually inspect before each use; on any of the following, retire immediately and cut it up so it cannot be reused by mistake:

• Label missing, damaged or unreadable — without a label there is no identity and no traceability;
• Cuts or punctures — into the load-bearing fibres, or longer than the maker’s limit;
• Wear exposing the core — surface fabric worn through, inner layer visible;
• Melting, charring or carbonisation — discolouration and hardening from heat or friction;
• Chemical corrosion — acid/alkali burns, brittleness, abnormal discolouration;
• Broken or opened load-bearing stitching — seams are the weak point for strength;
• Abnormal hardening, brittleness or obvious deformation;
• Knotting or forced shortening in the load-bearing area.

Beyond daily checks, schedule periodic inspections by frequency of use (at least annually for normal service, quarterly or even monthly for severe service) and keep written records. ASME B30.9 explicitly requires periodic inspection records, which US customers often audit.

9. Five-step selection

1. Weigh and locate the CoG: get the actual weight, mark the centre of gravity, confirm the number and position of lift points.
2. Fix the hitch: vertical, choker, basket or multi-leg? The hitch decides the factor.
3. Calculate max single-leg load: distribute the total by loading (four-leg = three-leg calc), then divide by the factor to get the required WLL.
4. Add the service-condition margin: sharp edges, high temperature, chemicals and frequent use each decide sleeve, material and whether to derate.
5. Finalise the spec: from WLL back-calculate width and ply, then length by lift-point distance; finally verify the label and colour coding.

10. Common misuse (with consequences)