"Pro Series HD Gen2 Xchangeable Flush Mount (XFM) lights are exchangeable from within the hull without hauling the boat. The XFM Gen2 lights combine a variety of quality marine grade materials, such as AB2 aluminum bronze and OceanLED's Tritonium™ coating allowing easy maintenance for annoying sea growth. Exceptionally low profile and unlimited hull mounting options with a very simple installation. Great solution for new installations as well as retrofit applications. Hole size: 4"."