I have a Platinum pocket pen with a slight problem: it doesn't take either converters or the standard Platinum cartridges because the barrel opening is too small. Here's the full body: http://extras.ourpatioparty.com/files/9914/4486/3419/Platinum_-_Full-640p.jpg And the open barrel: http://extras.ourpatioparty.com/files/7214/4486/3420/Platinum-Open_Barrel1-640p.jpg You see the threaded end has a metal 'rim,' preventing a normal cart from fitting. As I got it secondhand, it didn't come with 'instructions.' Any help or information you can give me on how to fill this will be greatly appreciated. Thanks!