WINDEX Wind Direction Indicators offer exceptional performance at the best value of any wind indicator worldwide. The secret is the sapphire jewel suspension bearing allowing the Windex 15 to seek relative wind direction in winds as little as 2/10th's of a knot. It also features a large fin - low inertia vane and easy-to-read, fully adjustable tacking tab system. Reflector tape on the vane and tacking tabs make WINDEX 15 easy to see day and night. WINDEX vanes are sturdy and when installed properly, offer many years of use. They have been wind tunnel tested to wind speeds of 80 knots!The WINDEX 15 has a 15" (38 cm) vane. Includes through-bolt or drill and tap mounting socket; 5/16" -18 stainless stud, washers and nut. Stands 12.75" (32 cm) tall and weighs just 3.9 ounces (111 g).