How to tie the Duncan Loop
by Norman Duncan
First grasp the end of the line and pull it through the thumb and forefinger of the opposite hand toward then around the base of the little finger to form a loop. Hold the two lines lightly with the same thumb and forefinger, pull the end out about 8 inches and circle around to create a loop with about 3 inches sticking out. Pass the end over the three lines and through the loop at least four times for mono over 100 pound test and successively more times with successively smaller line sizes. Pull the tag end and standing line together snug enough so that the knot will set and not loosen. Then put the loop on something smooth and solid like a small cleat or a gaff hook under foot. Grasp the tag end with pliers and the standing line with the other hand then apply equal tension on both lines in the same direction, pull slowly and hard to control the loop size until the knot folds over its self and snugs up to the desired tightness. The loop size can then be adjusted smaller by putting your pliers loosely against the top of the knot and pull the leader till it slips down. The tag end is cut off by pressing your cutters against the top of the knot between the leader and the tag end at about a 45 degree angle. When cut in this manner, the tag end will make a smooth slope from the leader to the knot and pass through the water without picking up as much grass or debris.
This knot has many possible applications, however it is limited by the low knot strength. In some types or brands of mono the knot strength may be as low as fifty percent depending on how well the knot is tied. If the leader strength is close to the line strength you may want to experiment with the intended application by testing as many of the various sizes, brands and number of turns combinations you expect to use. This can be accomplished by tying the knots then using a line testing machine or just weighing a bucket of water when each different knot combination breaks and recording the results. The best applications that I found for this knot are; it is the easiest knot to tie in very heavy mono, heavy mono or steelon tippet to the fly, loop on fly tippets, mono leader to live bait hooks or trolling lure, the knot can replace metal crimped sleeves.