This is for distributing sensitizing solution onto paper without losing any to a brush or sponge. I wanted a premade one (all glass) but they were out of stock.  I ordered some glass rods (10mm) and made a handle in TinkerCad that would fit a 10mm cylinder, glued it on and it works.  

How it works: you put some solution on the paper or whatever media you are using, press the glass part in the solution, allow the solution to work its way along the length, and then move it across the media to distribute it evenly. More/better instructions can be found wherever sensitizing solutions are sold (Bostick & Sullivan, Photographers Formulary, etc).