Review on Topnisus [Pack of 10] Clip-on Ferrite Core Ring Bead Cable Clip - Anti-Interference Filter for RFI EMI Noise Suppression, High-Frequency Optimization (5mm Inner Diameter) by Daniel Mandal

So I asked this question because after some time of searching for ferrites I still couldn't find an answer to the question "What size do you use for a regular headphone cable?" So I bought a 3mm and it works, although it slips a bit. You may have to find 2mm if it has them if it's a regular headphone. Of course if you have headphones (headset type) that you would use with stereo etc. mm can be a bit small One recommendation was to use shrink wrap or tape around the ferrite if it is too big.