Black Pressure Treated Wolmanized Wood Fence Post Caps 4x4 (3 5/8") Plastic post cap offer to protect the top of the wood post from water CAP PRESSES OVER THE OUT SIDE OF A 4X4 POST Easy to installed you can use a Nail, Screw or Glued the cap THE EXACT INSIDE DIMENSION OF THIS CAP IS 3 5/8" X 3 5/8". center mark where the hole can be punch either with the nail or drill small screw