An Introduction to Working Loads

Written By Rachel Novak


Minimum Breaking Strength (MBS) and Working Load Limit (WLL), formerly known as Safe Working Load (SWL), are two important strength ratings when it comes to rigging and safety equipment. They vary based on what type of rigging or safety equipment and are identified by manufacturers.


MBS is precisely what it says, the minimum amount of weight you can put on the equipment that would result in equipment failure. This manufacturer’s recommendation is its maximum weight load for lifting equipment.


Due to legal implications the US, and shortly after Europe, began using “working load limit” rather than SWL “safe working load”. However, they mean the same thing.  WLL or SWL is “the breaking load of a component divided by an appropriate factor of safety giving a safe load that could be lifted or carried.”


Both of these load numerical limits are assigned to lifting and/or rigging equipment. Overhead lifting equipment include hooks, shackles, straps, rope, line and equipment like cranes or other lifting devices. Manufacturers assigned a working load limit on these products.

The incorporation of various materials changes your working load limits. The strength of these materials is known as the mechanics of materials and deals with the behavior of solid objects and how they handle stress and strain.

The strength of a material is its ability to withstand an applied load without failure. A load applied to a mechanical member will induce internal forces within the member called stresses when those forces are expressed on a unit basis. The stresses acting on the material cause deformation of the material in various manner. Deformation of the material is called strain when those deformations too are placed on a unit basis. Therein lies the importance of knowing what materials are working with and what your load limits are for all equipment involved in your rigging and hauling.


There is a wide array of rigging accessories needed in hoisting and rigging. Henssgen Hardware is an industrial rigging hardware supplier. The rigging hardware we carry include: snap hooks, pulleys (fixed eye and swivel with single and double sheave), quick links, shackles, wire rope clips, drop forged clevis grab and clevis slip hooks.

Our rigging hardware is manufactured in stainless steel, solid brass, die cast zinc alloy, zinc plated malleable iron and zinc plated. All of our snap hooks are equipped with stainless steel springs. When dealing with expensive equipment, important loads and your safety, you must have quality hardware. Henssgen is committed to providing each one of our customers with the best.



  1. WLL stands for working load limit while SWL stands for safe working load.
  2. WLL and SWL are terms often used in the field of engineering.
  3. Safe working load is the older term of working load limit.
  4. The definition for safe working load is the breaking load of a component divided by an appropriate factor of safety giving a safe load that could be lifted or be carried.
  5. The working load limit is that it is the maximum mass or force which a product is authorized to support in general service when the pull is applied in-line, unless noted otherwise, with respect to the centerline of the product.
  6. Working load limits are calculated on straight line pulls only. Never side load. Other conditions such as extreme temperatures, chemicals solutions or spills, vapors, or immersion in salt water can reduce the Working Load Limit. Welds to any steel products can also void out a Working Load Limit rating.


1. Do Not load an assembly in excess of working load limits shown.
2. Do Not put an unequal load on one leg of a sling. Distribute the load evenly.
3. Do Not expose assembly to impact, rapid lifts or sudden stops.
4. Do Not tie knots or allow chains to become twisted.
5. Do Not use a chain that appears to be defective, worn or damaged.
6. Do Not fasten chain over sharp corners or edges. Protect with padding.
7. Do Not tip load hooks. The latch must never support the load.

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