The soft shackle is more than just a hunk of rope. There is actually a little bit of science behind what appears to be a simple loop. The shackle is first made by splicing the rope and stitching it so the eye can only open far enough to allow the ball end through. Then it is stretched on a tensile tester to the Working Load Limit. This will set the knot end and prevent it from becoming untied. For added protection the shackle is then re-dipped in a polyurethane coating and a piece of nylon chafe guarding is added.
The 9mm ones that Lucky8 sells have been tested on a 50,000lb tensile tester. This machine is calibrated by a third party every year, in part because the manufacturer must keep its test equipment up to date to comply with their military contracts.
The 9mm soft shackle is rated for a Working Load Limit of 18,000lbs. Today I had a brand new soft shackle tested and it broke at 26,088lbs. That is like hanging more than another Land Rover off the shackle past its Working Load Limit.
One thing to keep in mind with these shackles or any synthetic winch line is that they do have a shelf life. The manufacturer did a simulated long-term test of the shackle and these were the results:
First it was cycled 200 times from 14,000lbs - 20,000lbs. No damage. This should be close to the maximum pulling power of a 9k winch connected to a snatch block.
Then they upped the pulling power and kept on going. It took 73 cycles in the 20,000lb - 25,000lb range for the shackle to finally break at 25,182lbs. Keep in mind that the shackle was not allowed to cool down after each test as it was cycled continuously to test its durability in being loaded and unloaded repeatedly.
Here is some quick math:
If you were to go out twice a month and use the shackle at its maximum rating twice each outing, it would take you just shy of 6 years to mimic our testing. Not bad for a $25 shackle.
video of todays test.
I hope this helps put to rest some of the concerns that some people have had.