Windex 10 is the overwhelmingly popular choice for all dinghies and small keelboats.Sapphire jewel bearings: Popular around the world because they offer such an exceptional value, these wind indicators are super-sensitive to slight changes in wind direction at the masthead. They feature sapphire jewel suspension bearings, large fin/low inertia vanes and easy-to-read, adjustable tacking-tab systems for quick reference.Day or night visibility: Reflector tape on the vane and tacking tabs make Windex 10 Sport easy to see day and night. LED Light for Windex 15 and 10 Sport (sold separately) illuminates reflective reference tabs on the Windex.Wind tunnel tested: They have been wind tunnel tested to wind speeds of 80 knots!Windex 10 Sport has a 10" vane. Includes glass reinforced polycarbonate J-Base for side, top or front of mast mounting on most dinghies, smaller boats and sport boats. Stands just 9 1/4" tall and weighs 1.2 ounces.