By "didn't fit", did you mean it was too long? Or was it something to do with the nipple?
Thank you both for your questions and insight.
The converter fits into the section and feed without a problem.
It is the chrome-finished "sleeve" that is too wide for the inside diameter of the barrel.
As I mentioned above, I have the converters that came with my kits. I was just wondering why this one which came with a store bought pen, didn't fit. I thought there would be some type of standard among pens of a similar diameter and design. The store bought pen is this:
Nemosine Singularity Granite Fountain Pen | xFountainPens