Flange, - Mounting Hole,"4-1/2"- Color, Black "The Constellation compass features an internal gimbal ring that allows full tilt and heel, a virtually indestructible jewel, a hardened alloy pivot and a unique concave distant reading card that lets you read it from longer distances and at lower angles of sight. Designed for power or sail, these prestigious compasses provide uncompromising quality and performance for the most discerning yachtsmen. 4-1/2" dual reading card, featuring pantented no-spin global balance.",