Well, well, well… what do we have here? Is this an aerometric squeeze filler for small enough to fit inside a Kaweco Sport fountain pen? Why, yes it is!
Go forth and rejoice, all you Kaweco Sport users! For a mere $3 you too can now use bottled ink without having to reuse old cartridges or attempt to fill a cartridge with a syringe.
How to fill an aerometric filler: To use a aerometric squeeze filler like this, you put it on the pen first. First remove the old cartridge and place this on the pen, empty. Make sure its placed snugly on the pen. Squeeze the filler, then dip the nib into the ink bottle and slowly release to fill the bladder. You may need to to squeeze and release the filler 2-3 times to get it full. Just remember to squeeze gently so you don’t create bubbles or make a mess.