The Autopoint fountain pen uses a novel filling mechanism. There is a toggle or switch under the blind cap which is attached to two parallel bars connected by short hinged segments. Moving the toggle opens the bars into a parallelogram and then a full rectangular shape, compressing the sac. The patent for this “tab filler” US 1,733,780A (viewable at bottom of page) was issued October 29, 1929, one of the main dates of the stock market crash at the start of the Great Depression. Perhaps this inauspicious launch date explains part of the why so few are seen today.