Register key

On a saxophone, the octave key is positioned next to the left-hand thumb rest.

Pressing the octave key opens the top tone hole in the neck of the saxophone.

Some baritone saxophones, notably those made by Yamaha, also have three octave tone holes.

This involves extra keywork that frees the player from having to bother with an octave key at all.

The bassoon has similar keys used by the left thumb, but these are usually only depressed at the attack of notes, or "flicked".