Air Core Inductance.
A 1-Henry air cored inductor wound on a bobbin and capable of handling a current of up to 0.2-amps. Terminated with 4 mm banana socket.
(Wikipedia excerpt:.. “..The term air core (AC) coil describes an inductor that does not use a magnetic core made of a ferromagnetic material. The term refers to coils wound on plastic, ceramic, or other nonmagnetic forms, as well as those that have only air inside the windings. (AC) coils have lower inductance than ferromagnetic core coils, but are often used at high frequencies because they are free from energy losses called core losses that occur in ferromagnetic cores, which increase with frequency. A side effect that can occur in (AC) coils in which the winding is not rigidly supported on a form is ‘microphony’: mechanical vibration of the windings can cause variations in the inductance. …”)