3M 5200 quick cure. bed the fitting in it and then just draw the fitting up to the compound enough to form a gasket - go back the next day or so and tighten it up makes a perfect insulating gasket (of course I also put it in the screw holes - acts as a lubricant and later an insulator). Many will decry this method citing difficulty in removing the fitting, not to worry ...you can touch the screws with a large soldering iron for release - a micro torch will do the same thing. I hate mast fittings that come off at sea - these won't!