WLL, SWL and marking of lifting gear
To read the device's capacity and understand what the marking tells
Introduction
Lifting equipment is designed to carry a specific load and no more. The entire safety of a lift depends on knowing the equipment's capacity and staying within it. Therefore you must be able to read the marking and understand the terms on the equipment and in the manufacturer's tables.
WLL and SWL — what is the difference
WLL (Working Load Limit) is the largest load the gear may be loaded with in normal use. It is the figure you must stay below. SWL (Safe Working Load) is an older term that is being phased out in favour of WLL (BFA Industri). You can still come across SWL on older gear. BFA Bygge & Anlæg writes that both SWL and WLL express the maximum permitted load.
Fracture strength and safety factor
WLL is not the same as the load at which the gear breaks. The gear's breaking strength is far above WLL, and the ratio between breaking strength and WLL is called the safety factor. The built-in margin takes into account jerks, wear, uneven loading and material uncertainty. For this reason, you must never rely on the margin as extra lifting capacity — it is the safety reserve, not a buffer you draw capacity from.
The colour tells the WLL
Polyester webbing slings and round slings have a colour that shows the WLL. The colours follow the European standards for webbing slings (EN 1492-1) and round slings (EN 1492-2). The supplier CERTEX shows them like this:
| Colour | WLL |
|---|---|
| Violet | 1 tonne |
| Green | 2 t |
| Yellow | 3 t |
| Gray | 4 t |
| Red | 5 tonnes |
| Brown | 6 h |
| Blue | 8 t |
| Orange | 10 tonnes and above |
The colour is a quick help, but the label is the most reliable source. Polyester slings have a blue label sewn on. Single-use slings under the German standard DIN 60005 have an orange label. Fibre rope has a coloured marker thread: green is polyamide, blue is polyester, and brown is polypropylene. Polyethylene rope (orange marker thread) must not be used for lifting, because the material creeps under sustained load.
How to read the label
The marking or label on the equipment bears the information that makes it safe to use: the capacity (WLL), an identification that links the equipment to its documentation, and often material or class. Fiber slings are also color-coded according to capacity, so the right sling can be quickly identified. If the marking cannot be read, the capacity is unknown — and then the equipment must not be used until it is clarified.
| Equipment | The marking typically tells this |
|---|---|
| Chain | WLL, chain class and an identification for the certificate |
| Wire strap | WLL and an identification; capacity depends on suspension |
| Fiber sling (roundsling/band) | WLL, colour code for capacity and material |
| Shackles | WLL and size/type stamped in shackle and bolt |
Capacity depends on usage
The marked WLL applies to a specific use — typically a straight, simple pull. If the device is used differently, the capacity changes. If a strap is laid double or wrapped around the load, and hung from multiple points with spread, different figures apply than the simple WLL. The manufacturer's table states how the capacity is reduced for the way the device is actually used — and you use the table rather than guessing.
See the table of angles and capacity in the article on slinging and load assessment.
When the equipment doesn't have valid marking or documentation
Equipment without legible marking and without documentation has no known capacity. This also applies to homemade lifting devices and improvised brackets. Such equipment is taken out of service — not because it is necessarily weak, but because you do not know what it can bear, and therefore cannot safely lift with it.