A two-leg sling (also called a double-leg or bridle sling) is a permanent lifting assembly with two separate legs that connect to a load at two distinct points, converging at a single master link. While they provide excellent balance and stability for symmetrical loads like structural beams and machinery skids, failing to understand the physics of their sling angles can lead to catastrophic rigging failures.
The single, heavy-duty upper connection point that gathers both legs and interfaces directly with the crane hook or hoist.
Available in Alloy Chain (G80/100 for heavy, high-temp environments), Wire Rope (general heavy lifting), or Synthetic Webbing (lightweight for delicate surfaces).
The terminal components that attach to the load's lifting points, commonly featuring self-locking hooks, shackles, or grab hooks.
The most dangerous mistake in rigging is assuming that a two-leg sling simply has double the capacity of a single-leg sling.
Exponential Stress: As the angle between the two sling legs increases (spreading further apart), the actual tension and stress on each individual leg increases dramatically, reducing the effective safe lifting capacity.
The 60° Rule: If the included angle between the legs reaches 120° (which is 60° from the vertical plumb line), the tension on each leg is equal to the full weight of the load. At this exact point, the "extra leg" provides balance, but absolutely zero extra capacity.
Unequal Loading: A two-leg sling is only safe if the center of gravity is positioned directly under the master link. If one leg is shorter or the load is unbalanced, one leg will take the vast majority of the weight. This "Point Loading" can lead to the immediate snap of the overloaded leg.
Use of Adjusters: For asymmetrical loads where the center of gravity is offset, always use a Chain Shortener or an adjustable sling system to manually ensure both legs share the load tension equally.
The chart below demonstrates how a two-leg sling constructed from two 1,000 kg (1t) capacity legs loses overall capacity as the angle increases.
| Angle from Vertical (α) | Included Angle Between Legs (β) | Load Factor (M-Factor) | Actual Capacity Example (1t Legs) |
|---|---|---|---|
| 0° (Straight Vertical) | 0° | 2.0 | 2,000 kg |
| 0° to 45° | 0° to 90° | 1.4 | 1,400 kg |
| 45° to 60° | 90° to 120° | 1.0 | 1,000 kg |
| > 60° | > 120° | DANGEROUS | DO NOT OPERATE |
| Component | Safety Requirement | Action if Failed |
|---|---|---|
| Master Link | No physical deformation, stretching, or "ovality" | Replace Entire Assembly |
| Leg Length | Both legs must be of precisely equal length | Remove from Service |
| Coupling Links | Must move freely without binding or stiffness | Inspect Pins and Springs |
| Identification Tag | Must clearly show the WLL for specific angles | Re-Tag or Retire Sling |
