For boats to 39.4' (12 meters). 2-mile, 360 deg. visibility. Die-cast Zamak base with locking knob allows pole to be lowered to gunwale. Installation hole size: 7/8'' dia. 3 countersunk holes for #10 screws. 3/4" dia. brushed aluminum pole. Lightweight, high-impact plastic head. Frosted screw-on globe. Below deck clearance: 1''W x 24''D.