In this industry, the primary metals used in contact with coolant are Copper, Nickel, Stainless Steel, and Brass. These metals are considered safe together, having low galvanic potential between each other. Our coolants help mitigate these minor differences in potential. Aluminum and Zinc are two other metals that sometimes see use and contact with coolant, but will cause problematic galvanic corrosion when used with the other metals, therefore we heavily recommend against mixing them with the others. Hardware that uses aluminum that is not in contact with the coolant is absolutely fine.