Yamaha YEP-842S Owner's Manual page 5

Nomenclature
 Euphonium
Mouthpiece
Bell
Mouthpiece Receiver
Leadpipe
1st Valve Slide
Main Tuning Slide
Cap
Water Key
Cap
4th Valve
3rd Valve Slide
3rd Valve
Valve Casing
2nd Valve
2nd Valve Slide
1st Valve
 Top Action Tuba
Bell
Mouthpiece
1st Valve Slide
Leadpipe
Main Tuning Slide
Mouthpiece Receiver
Water Key
4th Valve
Valve Casing
3rd Valve Slide
3rd Valve
Cap
2nd Valve Slide
2nd Valve
1st Valve
5