Sheet bend
Knot
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The sheet bend is a bend knot. It is practical for joining lines of different diameter or rigidity.
It is quick and easy to tie, and is considered so essential it is the first knot given in the Ashley Book of Knots. Wikipedia
ABoK: (simple) #1, #66, #1431; (double) #488, #1434; (weaver's) #2
Category: Bend
Efficiency: 48%–58%
Names: Sheet bend, becket bend, weaver's knot, weaver's hitch
Typical use: joining two ropes of different diameters