The butterfly bend is a knot used to join the ends of two ropes together.

[2] The observation that the butterfly loop is secure enough to isolate a worn or damaged section of rope within the loop indicated that the bend form of the knot would be similarly secure.

[3] While the bend form had been known to mountaineers, nautical rigger Brion Toss brought the knot to a wider audience when he published it in 1975.

However, specific methods have been developed for tying the bend form directly, including the one shown below and characterizable using the mnemonic device "A d through a b; 'twixt the two and toward me": A properly tied butterfly bend should be as secure as the equivalent loop form.

[1] However, subtle positioning errors during the above shown tying method can result in a similar looking but insecure bend knot.