FERROXCUBE RFCHOKE FERRIT CORE with 10.6 mm inner diameter and so it is easly applicable on 10.4mm out diameter cables like RG8, RG213, RG214, Ecoflex10 etc. For smaller cable you can stick together more cores to increase the inductance. Recommended qty for RG213 and similar cable: 7MHz 10-15 pcs, 1.8-3.5MHz 20-25 pcs. It is working as an RF choke decreasing the common mode current on the shield of coax decreasing RFI problems both on TX and RX.
The Al-factor and 1 turn Z impedance FRQ charts of the ferrite core can be downloaded from the attached documents.