The most common metal used for spectacle frames, composed mainly of nickel, with the second largest component of copper, is:

Monel is a specific alloy primarily consisting of nickel, with copper as the second major component. It is well-known for its durability, resistance to corrosion, and ability to be easily shaped, making it ideal for use in spectacle frames. The combination of nickel and copper provides a strong and flexible material that maintains its structure under various conditions, which is particularly important for eyewear.

In the context of the other options, aluminum is lightweight and resistant to corrosion but is not primarily composed of nickel and copper. Nickel silvers, while they contain nickel and copper, also have zinc and lack the specific composition of Monel. Stainless steel, although it is a strong material used for frames, is made up of iron with chromium and nickel, differing significantly from the composition of Monel. This distinction in material content highlights why Monel stands out as the answer to the question.