Page 125 - Buck Tilton - Outward Bound Ropes, Knots, and Hitches 2 ed.

BOATING KNOTS: Stoppers

Double Overhand Knot

A COMPACT STOPPER FOR SMALL- TO LARGE-

DIAMETER CORD OR LINE

Not only a simple and useful stopper knot, the double
overhand works in all sizes of material, from thin thread to

thick cord. It shows up as a basis for other knots, including
bends, and can be tied in the end of lines to prevent fraying.

You will find it useful in activities other than boating. It is an
essential knot to know.