Hakko Replacement Magnet set for HK100 & 120. The magnet is the part that moves back and forth with the diaphragm therefore it has the role of holding the diaphragm secure. Normally the magnet is long-lasting, yet if you if you run the air pump with bad diaphragms for extended periods the magnet can deteriorate. If you open the motor for repair and find dust or small metal bits then this may be a sign that the magnet needs to be replaced. It is important to examine the magnet for wear and tear when replacing your diaphragms. These magnets can be very easily replaced.