From 8H to 8B, with three different charcoal hardness. Can come handy if you want to spice up a line drawing. Best viewed in inkscape. To add these to the dropdown list, check this tutorial: http://goinkscape.com/how-to-save-custom-filters-in-inkscape/
Minimal inkscape 1.0 extension https://github.com/costycnc/inkscape-1.0-python-hello-world-extension-costycnc