I designed this model for my pool safety fence to hold our two pool poles. It is a two-piece one-plate print optimized for hook strength. Print out of PETG. No supports needed.

The hook will friction slide into the cap. The cap will also friction slide into your fence post.

My fence post is 25mm round, so you may have to scale the model to fit over your post. Note that you will need to scale both pieces. I have not tested any scaled versions.