This assembly is designed to be used with the 3M Half Facepiece Respirators 7501, 7502 and 7503.The 3M Head Harness Assembly 7581, Respiratory Protection System Component, works with 3M Half Facepieces 7501, 7502, and 7503 (all sold separately). This harness is easy to install as a replacement part. This replacement part can extend the service life of respiratory protection equipment and potentially result in cost savings.