QUOTE(sara smith @ May 28 2008, 06:53 PM)

On the F side, you practise; on the Bb side of a high specification horn you have an extra valve that you depress for hand stopping.* If you don't have that valve, you stick to the F side for hand stopping, since on most of the pitches on the Bb horn the standard three don't give you the right adjustment.
* Your hand has to be fairly tight in the bell to get the right sound, and a small hand goes in further than a large one, so the amount of extra tubing you need varies. Having a dedicated valve allows you to adjust its tuning slide for this.