These are known as Ferrite Rod Loopstick Antenna Coils used in AM radios and Crystal ( Xtal ) Radio Sets. These are also known as a Antenna Coils, Ferrite Antenna Coils, Loopstick or Loop Stick , Magnetic Antenna Coil, Ferrite Rod Antenna Coils, AM ferrite Antenna Coils, Ferrite Rod Coils. Crystal Radio Antenna Coils. Crystal Radio Coils.
I sell these Crystal Radio Coils in two different values 680uh, 788uh. The 680uh comes in two forms one is on a round ferrite rod 10mm in diameter and 60mm long with no taps that is about 3/8 inches in diameter and 2-3/8 long. The other two are on flat bars 5mm X 12mm X 55mm long.