an effective barrier to the migration of particulate material into the critical interface region between the gin bar and the roller disc while the annular bushing 57 is bonded to a sidewall surface of the annular groove 34 as illustrated in fig4 c and 4d good service can be achieved with the bushing bonded onto a side surface of the annular rib 30 not illustrated the structure to which the bushing 57 is bonded is machined to the appropriate depth for receiving the bushing and bonding material and so that there will be positive non binding engagement between the annular rib 30 and the bushing 57 two preferred constructions for the roller discs 30 are illustrated in fig5 and 8 in fig5 the roller discs 26 28 are characterized by a circular planar face 60 fig1 and a smooth edge in the form of a cylindrical sidewall 62 as can best be seen in fig5 and 6 an alternate embodiment for the roller discs 26 28 is illustrated in fig8 in this embodiment each roller disc 26 28 is characterized by a circular planar face 60 and a smooth cylindrical sidewall edge 62 with the exterior face 60 of each disc being intersected by radially extending serrations 64 thereby defining alternating lands and grooves 64a 64b which in combination form an undulating outer periphery on the disc face 60 this undulating border on the disc face 60 substantially reduces the degree of friction which occurs at the ginning point thereby eliminating much of the wear on the roller disc which would ordinarily result when the lint.