These are stock clarinet thumb tubes that have been gold plated. Some musicians find throat tones, particularly open G, to have an improved tone when the thumb tube is gold plated. Some prefer the feel of gold. Some notice reduced skin irritation. Some notice their personal chemical makeup doesn't eat through gold like it does on silver/nickel. Some just think it looks cool.
These are make/model specific. You must order for your specific make/model of clarinet.
These must be professionally installed. This service is free when purchased through NCW (you just need to get your clarinet to me).