I use Staedtler Mars Matic technical pens, and while I love the pen, refilling the ink is almost always the harrowing experience of trying not to spill the ink when refilling the reservoir.

So I designed and printed a funnel that friction fits into the ink reservoir. The funnel’s neck is fluted to allow air to escape while the reservoir is being filled with ink. The sides of the funnel are hexagon shaped for an easy grip.

Let me know how it works for you.

Note: this will not fit ink reservoirs for other technical pens. I have brand-specific models for r0tring and Staedtler available.