The file '2×4 Post Cap 3D Printer Model' is (stl) file type, size is 2.4KB.
I couldn't find a Post Cap for a 2x4 anywhere at the local big box stores, so I just whipped one up and printed it.
I personally used these at the end of a 2x4 that is 10 feet long standing vertical to protect the end. I use a pair of these at the end of my 6 foot tall privacy fence to hold my ham radio antenna.
2x4_Top_Cap.stl | 9.0KB |