Ritchie compasses provide optimum illumination of the dial and lubber lines without hot spots or loss of night vision. The true spherical shape of the dome and bowl allows the dial and gimbal assembly to rotate smoothly for heel, pitch, and yaw motions while minimizing turbulence in the damping fluid. Domes provide clear, accurate magnification and are made of heavy-duty, optically clear polymer that prevents sun crazing and cracking. The O-ring seal is a custom Nitrile rubber. The dial assembly is gimbaled in a two-axis system where exact tolerances are maintained for smooth motion. The entire assembly is held level with a counterbalance. Only high Gauss magnets that are field-balanced to seek and lock on to magnetic north are used. The heart of all Ritchie compasses is the triple cup sapphire jewel and hardened steel pivot - no plastic here. 5° cards. Navigator Series features 4.5'' PowerDamp cards with built-in compensators, 45° lubber lines, 12V lighting, and reinforced Valox bowl. Five-year warranty. Mounting Hole Diameter: 4.75"" Finish: Black | Ritchie Navigator Series FN-201 Traditional Compass