an apparatus for heat - sealing thermoplastic materials includes a sealing jaw with a groove in which a thermal strip is mechanically anchored . the flange portions of the jaw projecting on either side of the groove are compressed towards one another and toward the thermal strip to thereby anchor the thermal strip within the groove . the sealing jaw is manufactured from aluminum which has been surface anodized to create an electrically insulating layer between the body of the jaw and the thermal strip .