It has been generally accepted that amperage and voltage are the only variables used to determine spray rate with the twin wire arc spray process. This belief has led to the common practice of defining spray rates in terms of kgs (pounds) per amperes. The "pounds to amperes" theory has been disproved with die advent of equipment capable of successfully arc spraying 4.8 mm (3/16 inch) diameter wires of zinc, aluminum, or 85/15 (zinc/aluminum). Changes in equipment design, that allowed the use of the larger diameter wires, resulted in the issue of a U.S. patent for arc spraying wires over 3.2 mm (1/8 inch) diameter. To achieve production capabilities for spraying 4.8 mm (3/16 inch) diameter wire, numerous problems needed to be solved, which led to additional patent claims.