J.w. Winco 50.5-nd-63 retaining magnet assembly disc-shaped w/ tapped hole – 2.48″ diameter, steel gn 50.5 magnets are a shielded magnetic assembly. To ensure that the magnetic forces are not impaired, the mounting screws must be made of non-magnetic material. For magnets with d1 diameter /= 50 mm, the magnetic surface of the magnet is covered with a plastic resistant to 175f (80c).