Flemished Eyes are Safer than Turnback Eyes | Wire Rope Sling Strength Discussion & Break Test

There are two popular types of swaged eye terminations for wire rope slings: a Flemished (aka Molly Hogan) eye, and a duplex/turnback eye. Each uses a type of swage sleeve, but only the Flemished eye is truly "spliced," making it a superior eye type for lifting slings.
Note: in this post, we discuss "termination efficiency," which is simply a measurement used for different types of wire rope ends that expresses the expected strength of a termination as a percentage of the wire rope's published breaking strength. If you have an eye type that's rated for 90% efficiency, used with a 1,000-pound breaking strength rope, your eye should hold to 900 lbs. Often, safety factors are worked into this as well, but today we're testing to failure, not illustrating appropriate rigging rules. Please keep this in mind as you review the video!
A properly installed duplex eye, based on Crosby S-506 sleeves, should achieve +/- 94% efficiency. That number seems fine at first, but the problem with duplex sleeves is that you have no inherent reserve capacity. If the sleeve is flawed, if it’s not properly swaged, etc., you may experience premature sling failure.
Conversely, Flemished eyes have reserve capacity, and that’s what we want to demonstrate here. Even if the eye is improperly swaged, or the sleeve has a material defect, the splice itself yields about 80% efficiency. Now, when properly done, a Flemished eye and a duplex eye will have similar efficiencies. But again, you have no redundancy, no “back-up” with a duplex eye like you do with a Flemsihed eye.
The reason for this is that Flemished eyes are spliced, as in braided, prior to being swaged. Duplex eyes (aka turnback eyes) are done by simply folding the line over on itself and swaging it into place.
To prove all of this, we will show y'all how well the Flemished eyes hold without the swage sleeve, and then we'll compare them to Flemished eyes done properly - and before we go any further, ⚠️ PLEASE NEVER USE A SLING WITH A FLEMISHED EYE THAT HASN'T BEEN SWAGED. We are only doing this for demonstration purposes.
Here are the facts:
We used 1/2" 6x26 IWRC RRL Bright wire rope;
Rope catalog breaking strength is 26,600 lbs;
A properly swaged Molly Hogan eye with this rope has a vertical/straight pull Working Load Limit (WLL) of 5,000 pounds (with 5:1 safety factor);
In a properly finished and swaged Flemished eye sling, we would expect it to fail at approximately 25,000 lbs. of force.
In our test, we found that the spliced but unswaged Flemished eyes held all the way up to 21,307 lbs., which is almost 85% termination efficiency. Again, ⚠️ NEVER USE AN UNSWAGED SLING!
Our test sling failed by the wires simply pulling out of their splice, as anticipated. With nothing to hold the tails in place, they were bound to pull out.
By comparison, our properly spliced and swaged Flemished eye slings (second test in the video) failed at 25,403 lbs., which is higher than its advertised breaking strength (25,000 lbs.). Its point of failure - several strands of wire broke near the base of the sleeve.
This is why we rarely use duplex/turnback eyes in our shops. There are specific applications where duplex sleeves are required, and our teams are well-equipped to install them correctly for safe use in the field. That said, given the option, we always prefer Flemished eyes, and these tests demonstrate why.
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