The light comes with a nice template / gasket. You need to drill the proper size holes as marked on the template. There is a brass collar that when tightened swedges the light to the deck. Don't take the collar too loose, the swedge is small and easy to misplace. I should have attached the wiring prior to installation. It was a tight squeeze to crimp the wires up in the bow of the boat, but after a few attempts it looks good.
very strange construction. mounts to boat with two sided "sticky tape. the screw that holds the lens on screws into a small brass sleeve that is loose and easily misplaced. The bulb socket contains three different pieces and those pieces can come out when you change the bulb. This may work fine but at best it is an unusually complicated way of doing something simple.