Shackle Size Chart & Working Load Limit
Picking a shackle by guesswork is dangerous. A shackle that is too small can fail under load, and a shackle that is too big is wasted weight and cost. The right way to choose is by the working load limit (WLL). This guide explains WLL, gives a reference size chart, and shows how to choose the correct shackle for your lifting job.
What Is Working Load Limit (WLL)?
Working load limit, often shortened to WLL, is the maximum load a shackle is rated to lift or pull in normal service. It is the number you must not exceed during use. WLL is not the same as the breaking strength: the breaking strength is the load at which the component actually fails.
WLL vs Breaking Strength
The difference is a safety factor. A shackle with a breaking strength of 5 tonnes may carry a WLL of only 1 tonne, giving a 5:1 safety factor. Rigging standards generally require a safety factor of 4:1 to 6:1. That margin covers shock loads, uneven loading and wear over time. Never use breaking strength as your working figure.
Shackle Size Chart
Shackle size is described by the pin diameter, and WLL increases with it. The table below shows common WLL values for US-type screw pin shackles. Use it for selection only, and confirm against the stamped WLL on the shackle and the manufacturer certificate.
| Pin Diameter | Metric | WLL (tonnes) |
|---|---|---|
| 1/4" | 6 mm | 0.5 |
| 5/16" | 8 mm | 0.75 |
| 3/8" | 10 mm | 1 |
| 7/16" | 11 mm | 1.5 |
| 1/2" | 13 mm | 2 |
| 5/8" | 16 mm | 3.25 |
| 3/4" | 19 mm | 4.75 |
| 7/8" | 22 mm | 6.5 |
| 1" | 26 mm | 8.5 |
| 1-1/4" | 32 mm | 12 |
| 1-1/2" | 38 mm | 17 |
| 1-3/4" | 45 mm | 25 |
| 2" | 51 mm | 35 |
How to Measure a Shackle
The key measurement is the pin diameter, because it determines the WLL. To measure, remove the pin and measure its diameter with a caliper. You can also measure the body diameter of the bow, but the pin size is the standard way to identify a shackle. A 3/8" shackle means the pin is 3/8" (10 mm).
Bow Shackle vs Dee Shackle
Shackles come in two main shapes:
- Bow shackle (anchor shackle): a wide, rounded "O" shape that can take loads from multiple directions or hold several slings. Use it for general lifting.
- Dee shackle: a narrow "D" shape for a single, straight-line pull. Use it where side loading is not expected.
For the same pin diameter, a bow shackle and a Dee shackle have the same WLL, but the bow shape is the safer choice when the load direction may vary. See our US type bow shackle and US type Dee shackle for examples.
Safety Factor and Inspection
Before every lift, inspect the shackle. Check that the pin threads fully, the body is not bent or stretched, and there is no cracking, corrosion or excessive wear. A stretched or distorted shackle has lost its load capacity and must be taken out of service. Always follow the safety factor and inspection rules in your lifting plan.
How to Choose the Right Shackle Size
Work through these steps:
- Calculate the maximum load, including any dynamic or shock loads.
- Multiply by your safety factor (for example, × 5).
- Pick the shackle whose WLL meets or exceeds that figure.
- Confirm the pin fits the attachment point and the sling eye.
- Verify the WLL stamped on the shackle and the material certificate.
As a rule of thumb, never size a shackle exactly to the load. Always leave margin.
FAQ
What does shackle size mean?
Shackle size refers to the pin diameter, such as 1/2" or 13 mm. A larger pin means a higher WLL.
What is the WLL of a 1/2" shackle?
A standard US-type screw pin shackle with a 1/2" pin is commonly rated around 2 tonnes WLL. Confirm with the manufacturer's rating.
Can a shackle be side-loaded?
Dee shackles should only be loaded in a straight line. Bow shackles tolerate multi-directional loading better, but avoid sharp side loads where possible.
Rigging Shackles Built to Standard
SolidLink forges bow, Dee and other shackles in carbon steel and stainless steel, with WLL marked and material certificates available. Browse our shackles category or contact us to confirm the right size for your load.
