This a Winch Post Protective Cap for 3 x 4 boat trailer vertical winch posts. Using a Winch Post cap prevents water and corrosive materials from entering the inside of your winch posts, which could ultimately rust it from the inside out. Also, the edges of winch posts tend to be very abrasive, and using this heavy-duty cover cap will protect yourself and others from catching on the edges. This Cap is for vertical 3 inch x 4 inch winch posts. This cap is not designed for angled winch posts. You can also use this to cap off any 3"x4" tubing where you don't want debris to get into.