This adapter will allow you to use our lights if your drain plug is plastic and not 1/2" pipe thread. Watch the video for a complete explanation. You will only need this adapter if you have a plastic drain and the threads are 7/8"inch. This adapter has a female 1/2" NPT to allow use of our lights with no modification to your drain IF you have a plastic drain plug! You DO NOT need this adapter if you have a regular 1/2" NPT (pipe thread). It works like your existing plastic drain, allowing you to drain the boat/bilge without removing the light.