These earphone elements are the moving coil type, which are components of various headband and helmet-type headsets (and, where applicable, telephone handsets), which are a part of the Intercommunication Set AN/AIC-1 OQ. They provide communication for both ground-level and altitude applications as specified (see 3.1). These parts have been approved by the Air Force Materiel Command, Human Systems Center, Armstrong Laboratory, Bioacoustics and Biocommunications branch (AL/CFBA), Wright-Patterson AFB, OH, as meeting United States Air Force safety and hearing-protective standards for such equipment.