For use in baluns and line-isolators. More than enough for UK legal power so perfect for your QRO balun project. 8 turns of RG8mini/RG58/RG316 (400w SSB) or RG142 (1kW CW/Digi) make a great "resistive" balun/choke for 5-30MHz. If you operate on 160m or 80m, consider using an FT240-31 for increased choking impedance.
The chart in the second image shows the number of turns and which ferrite is effective at HF frequencies. We also sell this size in 31-mix (1.8-30MHz) and 61-mix (UnUns), and 75-mix (VLF). There is also a 2.9" (73mm) version, aka: FT290-43 available here.
Need help choosing a ferrite? See our page on selecting the best size/type here.
Toroid sizes/types are easy to ID, the "240" translates to 2.4" (diameter) and the "43" is the ferrite mixture. What type do you need? 43 is good from 5MHz and up (and a good general-purpose 5-30MHz solution) while 31 is good for lower HF bands. Remember, you can stack the cores for increased choking and power-handling. As always, ratings need to factor in the aerial (SWR) match and duty-cycle.