A coil or coils usually constructed with cores having low magnetic reluctance, whose primary purpose is to furnish an inductive impedance in power or audio frequency circuit ranging from zero to 20 kilohertz (kilocycles). Includes audio frequency and power filter chokes, audio reactors and swinging chokes. Does not include transformers or coils used above audio frequency range. Excludes saturable reactor. For reactors with air cores, see coil (as modified).