We have vinyl plastic fencing around our backyard and the gates have these spear point fence caps. A few of them have broken off over the years so I designed these for replacements to match the old ones. They look almost exactly the same, just obviously brighter and newer. The fence posts that they fit on are 7/8" x 1 1/2" (so like 23 mm x 38 mm). These probably should be printed in ABS for outside conditions.
I printed it standing up straight and just needed support for the inside touching the build plate. I should probably also note that I over sized the opening by just a little because my printer is not perfectly calibrated. Someone else may need to size this down by 1 or 2% for it to fit tightly.