#31 material made by Fair-Rite Products is extremely useful, especially if your problem is below 5 MHz. By comparison to #43 material, #31 provides nearly 7 dB greater choking impedance at 2 MHz, and at least 3 dB more on 80 meters. At 10 MHz and above, the two materials are nearly equivalent. A feed-line choke made with #31 material is the best all round performer to cover all HF bands, and is clearly the weapon of choice at 5 MHz and below.
Jim Brown K9YC has published a must read Guide to RFI, Ferrites, Baluns, and Audio Interfacing. If you experience RF interference problems, read Jim’s A Ham’s Guide to RFI, Ferrites, Baluns, and Audio Interfacing.