This foot has two channels that run through the center of the foot on a slight angle.  This allows the foot to stitch as close as it can to the zipper teeth for the perfect invisible zipper.
 
 7mm machines (Most top loading models)  MW, DC series, skyline S3, jem, memory craft 6600p, 6500p, 5200, 4900, 3500, sewist, MS, cs995
9mm machines MC8200, MC9450, MC9410, CM7, CM6, S5, S7, S9, MC9850, 6670,6650, 12000