In regards to the end cap, I got the idea from this tutorial for using Pilot G-2 refills in Retro 51: http://geekandgirliestuff.blogspot.com/2015/12/retro-51-pen-with-g2-pen-refill-hack.html The guide says "The
Look out specifically forParker refills that comply with the ISO 12757-2 standard, then? This is interesting. The Quinkflow refills do not fare well in the tests even though they are certified. https://www.fountainpennetwork.com/forum/topic/316088-ballpoint-refills-test/ Question ...