Let´s talk about exhaust nuts a bit. The resistance to weathering is much higher for copper and copper alloys than for steel.
Galvanized nuts are also not an option since the zinc layer usually burns or oxidizes very quickly under the high heat loads. When exposed to heat, steel oxidizes much faster than at room temperature.
Therefore, loosening a copper nut on the exhaust pipe after a long time is no problem. Steel nuts tend to rust and in the worst case the stud bolt or screw will break off when loosening.
The nuts I´m using here are also coming with a collar perfectly fitting to the exhaust clamps and to increase pressure on these. So, please do yourself a favor and never use pure steel nuts!!!!!!