Abstract: A yarn fault detector suitable for mounting on a main frame of a knitting machine or on a side creel. The detector has two yarn guides on a guide frame that is biased to an operative yarn guiding position but movable overcenter to a yarn releasing position. End portions of a freely pivotable stop bar contact the yarn guides in the operative position of the guide frame to assure adequate contact with both guides. A variable bias is applied to the guide frame by means of a loop of flexible material on a rotary shaft, and a spring under tension between the loop and an eccentric cranked portion of the guide frame, the tension being dependent on the length of the loop wrapped around the shaft by rotation of the shaft. The loop and shaft are made by a one-piece moulding operation.