Timpani
The timpani was first introduced to the orchestra in the 17th century. It is also referred to as a kettle drum because of its rounded shape and is manufactured using either fiberglass or copper. The drum itself is tuned by tightening or loosening the bolts around the rim.
Timpani Keys
Sound is created on the timpani by striking the membrane of the instrument with a mallet. The tone or pitch can be adjusted to provide a rich array of sounds in an orchestra arrangement. To tighten the bolts around the rim of the timpani you need a special tool which is referred to as a timpani key. Most are shaped like a squat "T" which has a bolt opening at the bottom.
The Proper Pitch
Finding the proper pitch for your timpani is a complicated task. You need to have a trained musical ear and a familiarity with the instrument you are playing. You can find the proper pitch by humming into the membrane of the timpani. If the drum is in tune the membrane will vibrate at the sound of the pitch. If it isn't you should hum up slowly then down slowly. Depending on when your drum vibrates you will know which way you need to adjust it using your timpani key.