This is a scaled up version of a push pin. You may know it by another name. It is designed to use a ¼" diameter nail as the spike, available at any hardware store.

The profile I added uses variable layer height. A relatively small layer height was necessary to get the top bit to print due to the overhang. I also added variable layers to the top part of the rounded base to prevent excessive visibility of the lines, but I haven't test printed that yet.

I will likely do another one of these using the largest nail I can find.