Basically a simple clamp that holds a pen, sharpie or anything that is slightly less than 5/8 inches. This specific one goes on a shaft that is .5 inches in diameter.
Printed the holder upright. Used Layer Editing but this is optional. Print took 16 hours to print at 30mm/s with 40% Cubic infill and 4 wall perimeters. 3 pieces of hardware needed. 1/4X20 1-1/4 inch Carriage bolt, corresponding wing nut, and wing bolt (any size, you can tap the preexisting hole to your specs).