Abstract: In a pleat forming machine, apertures are defined in a pleat simultaneously with the formation of the pleat. A pusher bar carries a cutting member which projects into a recess defined in a pleating bar when the two bars are brought together to form the pleat. By so projecting, the cutting member pierces the folded material between the bars to form the required apertures. Clean and accurate cutting is assured by providing a continuous cutting edge, at the distal end of the cutting member, biased at an angle relative to the mating surfaces of the bars in order to concentrate the cutting force at a small portion of the edge at the time of puncture.