For a multitude of reasons, it seems like the plastic stake on our solar lights are the first thing to break. This is sized for a steel pipe that is 21.5mm (inside diameter). It can be scaled up or down to get a snug fit. Print this in PLA or preferably ABS or PETG with a skirt (or a brim if you have adhesion problems). Make sure you rotate the drawing so the top flat end is facing down and no supports are needed.