How to Select the Right Shackle Size: WLL Chart & 6-Step Guide
Select a shackle where WLL ≥ leg tension, where leg tension = (gross load ÷ number of legs) ÷ sin(θ). Use a bow shackle for multi-directional loads; dee shackles for straight in-line pulls only.
Shackle WLL Size Chart (ASME B30.26)
Carbon steel screw-pin anchor shackles, 5:1 design factor. Breaking load ≈ 5 × WLL.
| PIN DIAMETER | WLL (US TONS) | WLL (TONNES) | BREAK LOAD (T) |
|---|---|---|---|
| 5 mm (3/16") | 0.33 | 0.15 | 0.75 |
| 6 mm (1/4") | 0.50 | 0.23 | 1.14 |
| 8 mm (5/16") | 0.75 | 0.34 | 1.71 |
| 10 mm (3/8") | 1.00 | 0.45 | 2.27 |
| 11 mm (7/16") | 1.50 | 0.68 | 3.41 |
| 13 mm (1/2") | 2.00 | 0.91 | 4.54 |
| 16 mm (5/8") | 3.25 | 1.47 | 7.35 |
| 19 mm (3/4") | 4.75 | 2.16 | 10.8 |
| 22 mm (7/8") | 6.50 | 2.95 | 14.7 |
| 25 mm (1") | 8.50 | 3.86 | 19.3 |
| 32 mm (1-1/4") | 13.5 | 6.12 | 30.6 |
| 38 mm (1-1/2") | 17.0 | 7.71 | 38.6 |
| 50 mm (2") | 35.0 | 15.9 | 79.4 |
Source: ASME B30.26 / Crosby & CM catalogs. Alloy shackles differ — verify manufacturer data.
6-Step Selection Process
- 1 Determine the gross load
Start with the lifted weight. Add 15–25% dynamic allowance for crane starts/stops, or 50% for marine/shock loading.
- 2 Calculate each leg tension
T = (gross load ÷ legs) ÷ sin(θ), where θ is the sling angle from horizontal. At 90° (vertical) sin = 1.0 — minimum tension.
- 3 Apply a design margin
WLL already reflects the 5:1 factor — do not divide again. For critical or repetitive lifts, select shackle where WLL ≥ 1.25 × T.
- 4 Choose bow vs dee
Multi-leg slings, crane hooks, swivel eyes → bow shackle. Straight in-line pull, <5° off-axis → dee shackle. Any angular load requires bow.
- 5 Choose screw pin vs bolt type
Screw pin: fast, mouse it in vibration. Bolt type (nut + cotter): required for overhead crane service and anywhere pin rotation is possible.
- 6 Pre-lift check
WLL marking legible, pin fully seated and secured, no cracks / deformation / pitting / heat marks, load on bow not pin.
Calculate required shackle WLL from load and sling angle
Shackle Size Calculator →Frequently Asked Questions
What size shackle do I need for a 5-tonne lift?
For a single-leg vertical pick, select a shackle with WLL ≥ 5 t. With a 1.25× working margin, choose WLL ≥ 6.25 t (19 mm / 3/4" pin, rated 4.75 US tons / 2.16 t). Add an angle factor if sling legs are not vertical.
What is the difference between a bow shackle and a dee shackle?
A bow (anchor/omega) shackle has a rounded body rated for multi-directional loads — use it for multi-leg slings and crane hooks. A dee shackle has a narrow D-body for straight in-line loads only; side-loading can reduce WLL by 50%.
What safety factor do ASME B30.26 shackles use?
ASME B30.26 requires a 5:1 design factor — the breaking load is at least 5× WLL. This is already baked into published WLL ratings; do not divide the WLL again at the jobsite.
Should I mouse a screw-pin shackle?
Yes, whenever vibration, load rotation, or duration could unscrew the pin. Thread 2–3 mm wire through the pin hole and around the shackle body. For overhead crane service, use bolt-type (nut + cotter) instead.
Which way should the shackle pin face?
The load goes on the bow — the pin only closes the gate. Never thread a sling through the pin hole or apply load directly to the pin.
Based on published standards data. Not a substitute for qualified rigger judgment. Always verify with manufacturer data.