Fairywill Sonic Electric Toothbrush Brush Heads Refills for FW-507/ 508/959 Soft. Compatible with the following models：Fairywill FW-ET507、FW-ET508、FW-ET659、FW-917、515、FW-ET507Black-420. Dentists suggest to replace toothbrush head at least every 3 months to avoid exceeding breed of bacteria.
eBay