What is a stethoscope chest piece made of?

Almost all medical equipment is made of stainless steel. It's a metal that is easy to sterilize and doeesn't react with most stuff. The flexible parts of the stethoscope are rubber or plastic tubing but, the part that actually picks up and transfers the sounds to the ears is usually either a plastic disk or, sometimes, just a hollow opening. Other types of stehoscopes, such as used by mechanics for listening to noises within mechanical devices (like engines and gear boxes and tanks, etc.) often have a metal probe that allows the user to access additional parts of the things he/she wants to listen to. Early stethoscopes were just wooden rods, a few inches long, with a flared end (sort of like an oversized Golf tee) that the doctor would place againgst the patient's chest and the other end to his ear.