Review on DOT Certified 4-Inch LED Trailer Tail Light Kit: Red and Amber Lights with Grommets, Plugs, and IP67 Waterproof Design - Ideal for RVs and Trucks by Geoff Cooper

Whatever other reviewers say, don't make the holes for these lanterns too big! The socket is sized to fit a 4 and 1/2 inch bore. After you cut the hole, insert ONLY the rubber grommet (the large black ring that surrounds the light) into the hole, making sure the grommet "fits" properly and the small flexible flange on the grommet over the hole protrudes. This flange slides through the hole, but it has to wiggle and pull a bit to get it all the way through and into place properly. Once the socket is installed in the hole, insert the light assembly into the socket. Some force is required to ensure the light is fully inserted into the sleeve. To remove the lamp, push from the rear (if you have access) or gently pry the lamp away from the socket with a plastic front trim tool.