Here are the results of some work on developing a Section that will work with both a JOWO #5 feed and a Schmidt PRS Rollerball. The Schmidt has a main body that has a larger diameter but the very front of the JOWO has a step with a larger diameter. The body of the Schmidt section is longer than the JOWO but the overall length is about the same, the JOWO has a longer threaded section. So, you make a Schmidt section and drill the nib end to fit the larger diameter end of the JOWO. The Schmidt will center on the main body diameter and the front rim of the PRS will cover the hole drilled for the JOWO feed. The JOWO feed will center on the front most hole. The picture below will hopefully better show the sections. This will allow you to quickly change between a PRS, JOWO or Schmidt #5 feeds using the same section. Just make sure you design your cap to clear all the options. These are for a M9 x 0.75 threaded front section. All the internal dimensions will work if you use a 10mm section thread and you will have a thicker wall for the converter.
Danny
Danny