In 1974, I took a position with Kaiser Steel, to help identify metallurgical coal resources on their 530,000 acres of minerals near Raton, NM. I had read an old USGS report about igneous sills that had invaded the York Canyon coal seam in their "Upper York Canyon" area. A core hole proved this old report to be correct. I recovered some great igneous core from the stratigraphic horizon that should have been coal.
I've kept this for all these years, it's just sentimental. So I plan to make an interchangeable topper from this, unless I screw it up.
I plan to square off both ends so that I can drill perfectly vertically to install a threaded insert or coupling. Then I plan to grind and sand off the top end so that it is rounded. Carborundum (wet/dry) sandpaper will do the job from past experience.