Neither the drafting arrangement nor the mule spinner can draw the fiber strand out into individual fibers. If this is required, opening rollers must be used. The principle is familiar from the licker-in of the card and is today deliberately exploited in new spinning processes, for example, in rotor spinning machines. A small, rapidly rotating roller, clothed with saw-teeth or needles, tears individual fibers out of the slowly moving feed material (sliver). This type of draft cannot be used in all conventional spinning systems, since it not only disrupts parallelization of the fibers already achieved but also completely eliminates the retention of the fibers in a strand. This leads to the necessity for a subsequent collecting device which is also straightening the fibers.