as a student, the following parts must be checked; The Binaural – the stainless steel part that extends from the tubing to the earpiece. The ear tips – either plastic, silicone, or other material that covers the metallic part that goes into the ear. The tubing – the rubber part that runs from the binaural to the diaphragm. The chest piece – is the part that holds the diaphragm or bell for a two-sided head. The stem- is the metal part that attaches the tube to the chest piece. The ball bearing – allows for switching between frequencies