Made of semi-metallic and resin, semi-metallic provides good heat-resistant performance, resin provides good friction force, effectively protect the brake disc.  SUITE FOR MODELS  M1 PRO / M1 / D1 / D2 / D3 / D3S / D2S / D4S * * * PLEASE NOTICE * * * Please check sizes of your Original Fiido Bicycle before buying some of Them have Different Version.