1The plastic post caps that fit 4x4 wood posts have an inside diameter of 3.58" * 3.58". Please take care to measure your fence size correctly first to make sure you choose the right post cap size. 2The pointed design of the post cap prevents rain from rolling directly onto the top of the wood post, reducing moisture build-up. The post caps also reflect UV rays, reducing direct sunlight on the wood and drying it out. 3Post caps can also add to the overall aesthetics of your deck and enhance the decor of your outdoor space. 4A plastic post cap is a protective device installed on top of a fence post that effectively prevents birds and squirrels from using their sharp claws to scratch a wooden post or fence. 5This easy packing method improves installation efficiency and reduces handling steps and time. Simply place the post cap on the wooden post and screw two screws into the small holes on both sides to complete the installation.