Nickel / German silver is very popular for the outer tuning slide tubes, again because of its more durable nature. Most professional level trombones, tubas, etc have nickel silver outer tuning slides. I think with my Sterling, the entire body is Nickel silver. All of the tuning slide legs are N / S, and unless they plate the inside of the tubes, those are all Nickel Silver as well. Some companies use Nickel Silver for the valve casings, which means when you put in a valve oil like hetman that can lift corrosion away, you end up with orange colored oil when you wipe down the pistons.