Bowline on a bight advocate the use of a figure eight twisted version of the Bowline on a bight. This knot can be used to provide a toe hold in the middle of a rope; to make an emergency bosun's chair; and to create an upper rope "block" to make a crude purchase by threading the rope round an anchor point and then back up through the loop. It is sometimes used in sport climbing to tie into two anchor bolts independently. This knot is convenient when a dependable loop is required but neither end of the line is available. It's also commonly used
Blood knot Blood knot A blood knot (barrel knot) is most usefully employed for joining sections of monofilament nylon line while maintaining a high portion of the line's inherent strength. Other knots used for this purpose can cause a substantial loss of strength. In fly fishing, this serves to build a leader of gradually decreasing diameter with the castable fly line attached at the large diameter end and the fly or hook at the small diameter end. The principal drawback to the blood knot is the dexterity required to tie it. It is also likely to jam, which is not a concern