Brake disc bolt Pro Bolt Stainless steel A4 in gold. Brake discs screw Triumph front The golden color is attached by a complicated and elaborate process called DLC (Diamond-like-Carbon). The diamond layers (carbon layers) are applied to the screw in several layers, making them unique. Made of 316 stainless steel, which offers the following benefits: - excellent strength - excellent corrosion resistance - high resistance to acids