A guide rail assembly has a serial arrangement of linked carriages movable by pull cord or string along the rail and provided for the fixing of hanging parts such as blind slats. At least two carriages serve as pull carriages and each has a locking receptacle, whereas the pull cord is provided with at least one locking part fixed thereon. Each locking receptacle for the locking part forms a locking fit transport-fixed in both pulling directions of the pull cord, but detachable by a pulling force instantaneously exerted on the pull cord.