uxcell Toroid Core, Ferrite Chokes Ring Iron Powder Inductor Ferrite Rings, Light Green Blue 4pcs, 23.8 x 47 x 18.2mm: Amazon.com: Industrial & Scientific
Amazon.co.jp: PATIKIL Ferrite Toroid Core 14mm x 8mm x 7mm 10pcs Transformer Induction Coil Ring Black : Industrial & Scientific