Abstract: An operating mechanism for the seal jaw in a package wrapping machine has an operating arm with means along its length to alter the length of the arm between two finite positions. The arrangement is such that the operating arm for the sealing jaw in the package wrapping machine can be controlled so that it can open to a higher position for large packages and yet also open to a shorter position for less high packages, thus, speeding up the operation of the machine so that it can accept a greater number of packages for any given length of time.