RochambeauxCaliber is a unit of measurement, most commonly used for firearms. These are bolt pens, reminiscent of the way cartridges are loaded and locked into rifle barrels, with approximate diameter of what would be called ".45 caliber" if it was a gun barrel.
For more info: https://en.wikipedia.org/wiki/Caliber
For more info: https://en.wikipedia.org/wiki/Caliber