Helmsman Compass Features: 3 3/4" CombiDamp Dial. Easily Installed, Fits 4" (10.16 cm) Mounting Hole. Click here to view a template of the mounting hole (NOTE: Be sure you print the template actual size). Adapter Rings Available. Sold separately. 6" (15.24) Retrofits Existing Mounting Hole for Model No. HF-72 order H-ABLK. Exclusive Built-in Green NiteVu Night Illumination. Built-in Compensators to Easily Adjust for Deviation. Scientifically Matched Sapphire Jewel and Hardened Steel Pivot Dial Movement. Powerful DirectiveForce Magnets for Fast Heading Lock-on. Movable Sun Shield. 45 Degree Lubber Lines. High Temperature Composite Construction for Extended Operating Range.