The distance that the mouthpiece fits into the receiver is also of importance. The design of this section should be as smooth as possible with no leaks in the valves and slides. The bore of the instrument is measured in this section. The bore of the instrument has some affect on general resistance. Rotary valves are generally machined from brass and nickel silver stock.
Nickel silver is more retardant to corrosion and is used commonly for valve casings.
Rotary valves are by far the most commonly used type of valve for horns today, followed distantly in popularity by piston and Vienna valves. The rotors are either machined from solid brass rod or are formed and machined from sheet brass and tube to make a lighter weight hollow valve. Piston valves are often made of Monel metal which is very wear and corrosion resistant. There are a number of basic designs as to how the valve section is laid out. The first branch and the bell tail follow the cylindrical section.