one or more drive rolls forming parts of the machines may be grooved to group centrally the entering threads without materially adversely impacting driving and crimping operations of the machines thread focusing components also may be employed upstream of the inlet areas application_number US 13118908 A description illustrated in fig1 4 is a pair of drive pulleys preferably in the form of nip rolls 10 a b for a stuffer box or other crimping machine 14 as detailed in the meyer patent rolls 10 a b introduce thread into machine 14 to commence the crimping operation in particular respective drive faces 18 a b of rolls 10 a b are spaced slightly by a small distance d 1 in fig1 creating an area in which the thread may be positioned generally positioning the thread in the central regions 22 a b of faces 18 a b i e remote from edges 26 a b and 30 a b produces greater regularity of crimping both by centering the thread for entry into compression chamber 34 and by reducing likelihood of the thread sliding from between rolls 10 a b and thereby losing its drive force fig1 shows a conventional mass of thread t 1 entering machine 14 when rolls 10 a b are spaced by distance d 1 fig2 by contrast illustrates a centrally grouped and probably larger mass of thread t 2 entering machine 14 notwithstanding maintenance of the minimum spacing of drive faces 18 a b at distance d 1 this result may be achieved by creating circumferential groove 38 in central region 22 a of drive face 18 a of roll 10 a thread may fill groove 38 during operation.