JSP Manufacturing 16 Pack Fence Post Plastic Black Caps 4X4 (3 5/8") Pressure Treated Wood Made in USA 16 PACK Fence Post Plastic Black Caps 4X4 (3 5/8") Pressure Treated Wood Made In USA Actual inside diameter is 3 5/8 x 3 5/8 Pressure Treated Wood Made In USA FC-4x4-BLACK-16