A draw tape bag apparatus passes a web of plastic material having edge notched hems in the opposite edges to receive closing tapes. A hem sealer unit seals the folded layers of the web longitudinally of the folded edge to form the hem. The sealer unit includes a drum unit rotatably mounted on a shaft. The drum unit includes first and second drum parts having coaxial peripheral surfaces. A heat concentrating and release tape is secured to each drum part. The adjacent intermediate ends of the drum parts have telescoping and mating fingers and receses. Separate adjustment screws are coupled to the machine frame adjacent each drum part. Each screw is coupled to the outer race of a ball bearing secured to the adjacent outer end wall of the drum part. The setting of the screw accurately locates the heat concentrating tape axially of the drum. Hot air nozzles are mounted externally to the drum parts in alignment with the tapes and heat the web passing over the tapes to heat seal the web layers in the hem.