Armstrong Stainless Brake Discs BKF523R. Armstrong Road Wavy Solid Brake Discs. Optimising performance with a more efficient area of pad contact compared to standard round discs. Laser cut from premium Japanese induction hardened stainless steel, diamond ground for the perfect finish, these discs not only look great but also offer lighter weight over standard OEM models. 1x BKF523R Armstrong Brake Disc. Product Type: Brake Discs. Inside Bore: 56.4mm. Hole Diameter: 8.5mm. You can send us a message by using the “Questions and answers” section towards the bottom of the page.