Universal, very durable knot. It is often used in sea fishing for tying large, forged hooks to thick fishing line. The difficulty of the knot is how to make and fix the first turn of the line, and then, when making a step, to prevent the loop from slipping out from under the first turn of the step. The secret is to press the line tightly to the hook with your finger, and tighten the second turn under the finger pressed tightly to the hook - then the turn will be securely fixed.