Researchers used a high speed video camera to study the mechanism of end breakage due to weaver's knots and fisherman's knots in cotton yarn during plain weft knitting. Results revealed that end breakage due to knots in the plain weft knitting zone resulted from knots jamming in the space between a needle hook and latch or an old loop and in the space between a needle head and a verge. The jammed knot rate and the end breakage rate for jammed knots increased with increasing depth of stitch draw, input tension, and takedown weight of the knot. Fisherman's knots produced higher rates of jammed knots, more knots, and higher end breakage rates for jammed knots than weaver's knots under all knitting conditions. 5 refs.