ADC Model 171-R curtain track is identical to ADC Model 170 except it employs No. 1749 Neoprene Ball-Bearing Single Carriers and No. 1750 Neoprene Ball-Bearing Master Carriers, which provide quieter operation and an easy to pull operating cord. These carriers are used in place of the standard No.1701 and No. 1702 standard polyethylene carriers.