A comminutor for shredding rag-like materials includes a frame member having a cutter bar that is affixed thereto and has a plurality of cutter teeth, and includes screen bars aligned with the cutter teeth. Each of the screen bars has an end that fits closely to its adjacent cutter tooth and the frame member so as to close a gap between the cutter tooth and the frame member. The end of the screen bar may include a flange that fits closely to the frame member and a tab proximate to the flange that fits closely to the cutter tooth. In an embodiment where the cutter tooth is flush with the frame member, the end of the screen bar includes a flange that fits closely to both frame member and the cutter tooth.