My reading on the subject has led to these conclusions:
- there is no true 'international standard' (ie, a consensus document that defines the dimensions to be used by various subscribing manufacturers). Instead, the 'standard international cartridge' is a design that was originally developed by Pelikan and that is used by many pen manufacturers who don't want the hassle of manufacturing proprietary sealed cartridges.
- sealed Pelikan cartridges come in both a short version (38mm, or 1.5") and a long version (72mm, or 2.8"). Both are nominally 1/4" in diameter.
- the main factor that is of concern is the ID and OD of the nipple that attached to the section. There are variations in these dimensions with the result that not all international cartridges fit all pens that supposedly use international cartridges.
- pens manufactured in Asia (and pens made from kits produced in Asia) tend to use a cartridge similar to the short Pelikan cartridge.
- sealed cartridges are not designed to be refillable, but it is possible to refill them using a syringe.
- most cartridge pens can also be fed using converters (aka 'pumps') that can be refilled by the user. A 'standard international converter' is longer than a 'standard short international cartridge, and it has a slightly greater diameter. However, the ID and OD of the nipple are theoretically the same as for a 'standard international', or Pelikan cartridge. Most converters are refilled using a piston mechanism (either advanced/retracted via knob at the end, or by sliding the piston in/out using a protrusion on the side. I've measured the diameter of a few - they range from 0.281 - 0.3125" at the widest point.
Final point: when fountain pens are made from kits, the cartridge/converter is contained within the brass tube in the body of the pen. The information I have indicates that the Sedona uses either a 10mm or a 25/64" tube, with an ID of about 0.357". So while there could be some discrepancy in the OD of the 'standard international cartridge', that dimension should still be less than the ID of the tube. So something is amiss in the description of the problem here how is it that either a cartridge or converter is not fitting inside that tube?