Glossary

Breaking strength is the load at which a component fails (breaks) when it’s tested to destruction under specified conditions. It’s a laboratory/qualification number—useful for engineering and comparison—but it is not the number you’re allowed to lift or load in the field.

In industrial rigging and fastener land, breaking strength is usually determined by a controlled test (often a straight, axial pull at a defined rate, with defined terminations/fixtures and environment). You’ll see it reported as minimum breaking strength (MBS), minimum breaking load (MBL), or ultimate tensile strength/load depending on the product. For wire rope, for example, catalogs often publish an MBS for a given rope construction and diameter; for synthetic slings and straps, an ultimate break value is typically part of qualification.

The key relationship is that rated load / WLL / SWL is derived from breaking strength by applying a design factor (safety factor). That factor accounts for variability in material, manufacturing tolerances, wear, damage, shock loading, fatigue, bending losses, temperature effects, and real-world misuse. So if a sling has a 5:1 design factor, its working limit is typically set around one-fifth of its minimum breaking strength (exact rules depend on the standard and product category). That’s why you can’t “work close to break”—field conditions are messy, and the whole point of WLL is to keep you out of the failure zone.

Also, breaking strength is condition-dependent. Change the setup and you change the result: a wire rope bent over a small sheave loses capacity compared to a straight pull; a knot in a rope reduces strength; a corroded cable has lower actual strength than catalog MBS; heat-treated bolts can fail differently depending on temperature and loading rate. In other words, breaking strength is a useful baseline, but it assumes the test conditions and the product in new or specified condition.

AKA: Minimum Breaking Strength, Minimum Breaking Load, Ultimate Strength