Abstract: Disclosed is an apparatus for closing open-topped flexible containers, the apparatus being of the type having a pair of movable gathering arms which can gather and compress the flexible material to a configuration, and at an appropriate location, suitable for applying a fastener to the gathered material. The gathering arms cooperate with fixed guide means to sweep the flexible material to the gathered location. The gathering arms and the guide means are shaped, and positioned relative to one another, such that, at each location in the motion of the gathering arms, they make at least a right angle with respect to both the adjacent guide means and each other, thereby reducing the possibility of damaging shearing action on the flexible material.