The search for a spring from a pen that fits an Iwata has always been a pain. And when you find one it is always in a no-name brand pen and you can not help people more then that. Well, till today. I found a well know branded pen that has the perfect spring. To start off with, it is pretty nice pen with a nice erasable feature. It's the Pilot Frixion Clicker. It sells for about $1.50 here in South Africa and are available in 5 or 6 colours. Not that the springs are any different in the various colours. I use them in the office so buying a few just for the springs are not a complete waste as I can just hold on to the refills. It is a bit shorter and softer than the stock spring. Just about the same diameter. This is on needle shaft of an Eclipse. I tried it on a HP-B and a Micron and the fit is exactly the same. On the Micron you have to turn the spring tensioner all the way in. It's got a very nice linear feel though out the whole travel of the trigger. I hope this helps someone.